/  2- 


BELT   CONVEYORS 


AND 


BELT    ELEVATORS 


BY 


FREDERIC  V.  HETZEL,  M.E. 

Member   American   Society  6f  Mechanical  Engineers, 
Member  Franklin  Institute  of  Pennsylvania 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 

LONDON:    CHAPMAN  &  HALL,  LIMITED 

1922 


Engineering 
Library 


V   «>    * 

.     .     .    « 

*  *    •  •J 


,  *  •>  *  *        r      •• 


Copyright,  1922,  by 
FREDERIC  V.  HETZEL 


PRESS  OF 

BRAUNWORTH  A.   CO. 

BOOK    MANUFACTURERS 

BROOKLYN,    N.    Y. 


PREFACE 


This  is  intended  to  be  a  practical  book.  It  is  not  a  mere  restatement  of 
what  already  appears  in  trade  advertisements,  nor  does  it  contain  descriptions 
of  installations  of  conveying  and  elevating  machinery.  It  aims  rather  to 
explain  principles  and  the  reasons  for  doing  things. 

The  present  volume  describes  Belt  Conveyors  and  Belt  Elevators.  These 
machines  are  so  generally  useful  and  suit  so  many  kinds  of  materials  under  so 
many  operating  conditions  that  they  are  used  to  illustrate  some  of  the  prin- 
ciples underlying  the  general  subject  of  the  design  and  use  of  conveying  and 
elevating  machinery  and  to  serve  as  an  introduction  to  that  subject. 

The  business  of  designing,  making  and  selling  such  machinery  is  hardly  more 
than  forty  years  old;  for  thirty  years  of  that  time  th'e  author  has  been  active 
in  it,  at  the  drafting  board,  in  the  shop,  and  in  the  field  supervising  the  erection 
and  operation  of  the  machinery.  For  thirteen  years  the  author  was  chief 
engineer  of  one  of  the  largest  companies  in  the  business,  was  responsible  for  the 
design  of  all  kinds  of  elevating  and  conveying  machinery,  and  acquired  valuable 
experience  in  dealing  with  suggestions  and  complaints  from  users  of  the  machin- 
ery and  in  co-operating  with  them  in  improvements  in  design  and  manufacture. 

The  aim  has  been  to  present  that  experience  in  such  a  form  as  to  be  useful 
to  men  who  have  material  to  handle  and  who  want  to  know  more  of  the  "  how  " 
and  "  why  "  of  conveying  and  elevating  by  belts  than  can  be  told  in  the  catalogs 
and  advertisements  of  manufacturers.  The  information  given  will  be  of  use 
also  to  consulting  engineers  who  have  to  advise  in  the  selection  of  the  proper 
machinery  to  do  certain  work,  to  engineers  and  draftsmen  who  design  such 
machinery,  and  also  to  students  in  technical  schools  and  colleges. 

Much  of  the  information  published  in  this  book  has  never  appeared  in  print 
and  for  a  great  deal  of  it,  the  author  is  indebted  to  his  friends,  some  of  them 
business  associates,  some  of  them  business  competitors.  To  each  of  them  he 
returns  his  sincere  thanks. 

West  Chester,  Penna.  FREDERIC  V.  HETZEL. 

June  3,  1922. 


iii 

531)773 


*  CONSENTS 


SECTION  I.    BELT  CONVEYORS 

CHAPTER  I.     GENERAL  DESCRIPTION  OF  COMPONENT  PARTS 

PAGE 

Elements  of  a  Belt  Conveyor 1 

Brief  Description  of  Parts 2 

Belt  Conveyor  Accessories 3 

Specimen  Arrangements 4 

CHAPTER  II.     DEVELOPMENT  OF  BELT  CONVEYORS 

Early  History  in  the  United  States 6 

Westmacott  and  Lyster's  Work 7 

Development  of  Grain  Conveying 8 

Conveying  Materials  Heavier  than  Grain 10 

Improvements  by  Thomas  Robins 11 

Early  Difficulties 14 

Changes  in  Belt  and  Idler  Construction 15 

Reinforced  Belts 19 

CHAPTER  III.     BELTS  AND  BELT  MANUFACTURE 

Manufacture  of  Rubber  Belts 20 

Compounding  of  Rubber 21 

Kinds  of  Rubber  Belts 22 

Edge  Construction 24 

Rubber  Covers 25 

Resistance  of  Rubber  Covers  to  Impact  and  Abrasion 26 

Reinforced  Covers ' 29 

Specifications  for  Rubber  Belts 30,  37 

Comment  on  Specifications 32,  38 

Method  of  Testing  Fabric 33 

Method  of  Testing  Friction 35 

Method  of  Testing  Finished  Belt 39 

Improvements  in  Rubber  Belts 41 

Weights  of  Rubber  Belts 42 

Flanged  Belts 43 

Effect  of  Light,  Heat  and  Age  on  Rubber 44 

How  to  Keep  Rubber  Goods 46 

Stitched  Canvas  Belts 46 

Saturating  Compounds  for  Canvas  Belts 47 

Flexibility  of  Stitched  Canvas  Belts 49 

Balata  Belts 50 

Solid-woven  Cotton  Belts 50 

Strength  of  Belts 52 

Kind  of  Belt  to  Use 54 

Belt  Fasteners 56 

Belt  Splices 59 

Sandvik  Steel  Belts 59 

Steel  Mesh  Belts 62 

Steel  Rope  Belts 63 

V 


vi  CONTENTS 

CHAPTER  IV.    SUPPORTING  AND  GUIDING  THE  BELT 

PAGE 

Commercial  Troughing  Idlers 65 

Return  Idlers 69 

Side-guide  Idlers 69 

Spacing  of  Troughing  Idlers » 70 

Elevation  of  Pulley  Rims  with  Respect  to  Idlers 71 

Effect  of  Increased  Idler  Spacing 72 

Supporting  the  Belt  at  Humps  and  Bends 73 

Natural  Troughing 74 

Wear  of  Idlers 77 

Why  Belts  Run  Crooked 77 

Steering  Effect  of  Idlers 79 

How  to  Make  Belts  Run  Straight .  .* 81 

Internal  Stresses  Due  to  Troughing 81 

Troughing  Canvas  and  Balata  Belts 82 

Spool  Idlers  and  Flared  Idlers 83 

Flat  Pulley  Idlers \ 84 

Grease  or  Oil  Lubrication 87 

Ball-bearing  Idlers 88 

Roller-bearing  Idlers 90 

Advantages  of  Ball-bearing  and  Roller-bearing  Idlers 92 

Reduced  Cost  for  Power  and  Maintenance 93 

Idlers  with  Tapered-Roller  Bearings 95 

CHAPTER  V.     DRIVING  THE  BELT 

Horse-power  to  Drive  Belt  Conveyors 96 

Comparison  of  Formulas  for  Horse-power 99 

Tables  for  Horse-power 101,  105 

Reduced  Horse-power  Due  to  Improved  Idlers 106 

Long-distance  Belt  Conveying 107 

Relation  between  Horse-power  and  Belt  Tension 108 

Calculation  of  Belt-pull  and  Thickness  of  Belt 110 

Working  Tensions  for  Conveyor  Belts Ill 

Tension  in  Inclined  Belts 112 

Width  of  Belts 113 

Thickness  of  Belt  as  Determined  by  Troughing 114 

Design  of  Belt  Conveyors 115 

Faulty  design  of  a  Large  Belt  Conveyor 117 

Where  to  Drive 118 

Tandem  Drives 119 

Advantages  and  Disadvantages  of  Tandem  Drives 120 

Slip  and  Creep  of  Conveyor  Belts 123 

Pressure-belt  Drives 124 

Auxiliary  Drives 126 

Sizes  of  Pulleys 127 

Snub-pulleys  and  Deflector-pulleys 128 

Curves  in  Belt  Conveyors 129 

CHAPTER  VI.     TENSION  AND  TAKE-UP  DEVICES 

Gravity  Take-ups 131 

Screw  Take-ups 131 

Weighted  Pull-back  Take-ups 132 

CHAPTER  VII.     LOADING  THE  BELT 

Loading  Chutes 133 

Screen  Chutes 135 

Drip  Chutes 136 

Design  of  Skirt-boards 137 

Feeding  as  Related  to  Belt  Capacity 139 

Belt  Conveyor  Feeders 140 


CONTENTS  vii 

PAGE 

Traveling  Loading-hoppers ." • 140 

Loading  Inclined  Belts 141 

Dangers  of  Steep  Inclines 142 

Capacities  of  Belts  as  Affected  by  T  roughing 143 

Capacities  of  Belts  as  Affected  by  Operating  Conditions 145 

Capacities  of  Belts  on  Flat  Idlers  or  Flared^Idlers 146 

Peak-load  Capacities T 148 

Capacities  of  Grain  Belts 150 

Speeds  of  Belt  Conveyors 151 

Limitations  of  High  Speed 152 

Speeds  for  Inclined  Belts 154 

Speeds  for  Grain  Belts 155 

CHAPTER  VIII.     DISCHARGING  FROM  THE  BELT 

Discharge  Over  End  Pulleys 157 

Discharge  by  Scrapers  or  Plows 158 

Discharge  by  Trippers '. 160 

Fixed  Trippers 161 

Traveling  Trippers 162 

Self-propelled  Trippers 162 

Automatic  Self-reversing  Trippers 165 

Tripper  Pulleys 165 

Tripper  Chutes  and  Brushes 166 

Tripper  Trailers 167 

Trippers  of  Unusual  Design 168 

Length  Required  for  a  Tripper 169 

Location  of  First  Discharge  Point 169 

Depressed  Loading  Ends 170 

Increasing  the  Range  of  Dischaige 171 

Shuttle  Conveyors 173 

CHAPTER  IX.     PROTECTING  AND  CLEANING  THE  BELT 

Brushes  for  Cleaning  the  Belt 178 

Beaters  and  Scrapers 179 

Cleaning  Pulley  Rims 180 

Protective  Decks 180 

Design  of  Belt  Conveyor  Enclosures 181 

Importance  of  Accessibility  for  Lubricating  and  Cleaning 183 

CHAPTER  X.     PACKAGE  CONVEYORS 

Belts  for  Package  Conveyors 184 

Supporting  Rollers 185 

Package  Conveyors  for  Department  Stores 186 

Transfers  between  Conveyors 187 

CHAPTER  XI.     SPECIAL  USES  OF  BELT  CONVEYORS 

Portable  Conveyors 188 

Car  Loaders 189 

Throwing  Machines 190 

Conveying  between  Two  Belts 191 

Newspaper  Conveyors 192 

Conveying  and  Elevating  by  Rolling  Contact 193 

Picking  Belts 194 

CHAPTER  XII.     LIFE  OF  BELTS 

How  Long  Should  a  Belt  Last? : 196 

Causes  of  Belt  Failure 197 

Actual  Life  of  Certain  Rubber  Belts .  198 


viii  CONTENTS 

PAGE 

Costs  of  Handling  per  Ton 198 

Typical  Injuries  to  Belts 199' 

Life  of  Stitched  Canvas  Belts 201 

CHAPTER  XIII.     WHEN  TO  USE  BELT  CONVEYORS 

General  Advantages  of  Belt  Conveyors 202 

Comparison  of  Various  Conveyors  for  Boiler  Houses 203 

Comparison  of  Various  Conveyors  for  Other  Work 204 

The  Right  Choice  of  a  Conveying  Machine 205 


SECTION  II.     BELT  ELEVATORS 
CHAPTER  XIV.     GENERAL  DESCRIPTIONS 

Elements  of  a  Belt  Elevator ; 207 

Description  of  Parts 208 

Accessories 210 

CHAPTER  XV.     CENTRIFUGAL  DISCHARGE  ELEVATORS 

Pick-up  and  Discharge 211 

Theory  of  Centrifugal  Discharge 212 

Effect  of  Speeds  which  are  too  High 213 

Effect  of  Speeds  which  are  too  Low 215 

Belt  Speeds  Depend  upon  Nature  of  Material 215 

Effect  of  Centrifugal  Force  upon  Pick-up 216 

High  Speed  Elevators  for  Grain 217 

Moderate  Speed  Elevators  for  other  Materials 218 

Practical  Rules 218,  219 

Effect  of  Foot-wheels  which  are  too  Small 218 

Effect  of  Shape  of  Boot 219 

Elevators  for  Pulps,  Slimes  and  Liquids 220 

Photographs  of  Elevator  Discharge 223 

CHAPTER  XVI.     ELEVATOR  BUCKETS 

Discharge  as  Related  to  Shape  of  Buckets 225 

Discharge  as  Related  to  Spacing  of  Buckets 226 

Kinds  of  Buckets 227 

Sheet-steel  Buckets 228 

Malleable  Iron  Buckets 230 

Uses  of  Various  Styles  of  Buckets 232 

Buckets  for  Liquids  and  Pulps 232 

Spacing  of  Buckets  on  Belt 233 

Pick-up  as  Related  to  Shape  and  Spacing  of  Buckets 235 

Peak-load  Capacities 235 

Relation  between  Bucket  Capacity  and  Elevator  Capacity 236 

Overload  Capacity  of  Certain  Elevators  in  a  Concentrating  Works 238 

European  Buckets 239 

CHAPTER  XVII.     CONTINUOUS  BUCKET  ELEVATORS 

Loading  and  Discharge 240 

Shapes  of  Buckets .» 241 

Height  of  Buckets 243 

Capacities  and  Speeds 243 

Pulleys 244 

Loading  Legs 245 


CONTENTS  }x 

CHAPTER  XVIII.     BELTS  FOR  ELEVATORS 

PAGE 

Why  Elevator  Service  is  Severe  Work 246 

Grain  Elevator  Belts 247 

Wear  of  Belts,  External  and  Internal .-. 249 

Friction-surface  Belts,  Rubber-covered  B*elts 249 

Rubber  Covers fa 250 

Examples  of  Current  Practice  .  .T 251 

Choice  of  Elevator  Belts 252 

Belts  for  Wet  Elevators 253 

Belts  for  Continuous  Bucket  Elevators 254 

CHAPTER  XIX.     FASTENING  BUCKETS  TO  BELTS 

Single  Row  or  Double  Row  of  Bolts 256 

Pull  on  Bucket  Bolts , 258 

Spacing  of  Bucket  Bolts 259 

Damage  to  Belts,  where  Buckets  are  Bolted  on '. 260 

Protective  Devices 261 

Width  of  Bucket  and  Width  of  Belt 261 

Inspection  of  Buckets  and  Bolts 261 

Buckets  in  Double  Row 262 

Joining  Ends  of  Elevator  Belts 263 

CHAPTER  XX.     DRIVING  BELT  ELEVATORS 

Coefficients  of  Driving  Contact 266 

Effect  of  Dust  and  Dirt 268 

Calculation  of  Belt  Pull 269 

Calculation  of  Horse-power 270 

Pull  in  Belt  due  to  Pick-up 272 

Effect  of  Take-up  Tension 274 

Working  Tensions  for  Elevator  Belts 274 

Determination  of  Belt  Thickness : 274 

Belt  Slip  and  Belt  Creep 275 

Injurious  Effects  of  Slip  and  Creep 277 

Head  Pulleys 278 

Lagging  of  Pulleys 278 

Pulley  Rims 279 

CHAPTER  XXI.    ELEVATOR  BOOTS 

Fixed-bearing  Boots 281 

Concrete  Boots 282 

Take-up  Boots 283 

Boots  for  Coarse  Materials 283 

Dust-tight  Boots 284 

Position  of  Feed  and  Shape  of  Front 286 

Fly-feed  or  Scoop-feed 288 

Feed  into  Side  or  Back  of  Boot 288 

Objections  to  Small  Foot  Pulleys 289 

Material  Catching  between  Belt  and  Foot  Pulley 290 

Guards  Over  Foot  Pulley 290 

Elevator  with  No  Foot  Pulley 291 

Amount  of  Take-up  Travel 292 

Lubrication  of  Boot  Bearings 293 

Grain  Elevator  Boots 294 

Automatic  Weighted  Take-up  Boots 298 

Artificial  Tension  for  Vertical  Belts 299 

Causes  and  Prevention  of  Chokes  in  Elevator  Boots 301 

Safety  Devices 304 

Back  Stops 305 


X  CONTENTS 

CHAPTER  XXII.     INCLINED  ELEVATORS 

PAGE 

Loading  and  Discharging 307 

Path  of  Belt  on  Return  Run 307 

Calculation  of  Pull  in  Belt 308 

Calculation  of  Artificial  Tension '. 309 

Discharge  from  Spaced  Buckets 310 

Sizes  of  Pulleys 311 

Point  at  which  Discharge  Begins 312 

Sizes  of  Head  Wheels  and  Spacing  of  Buckets 313 

Advantages  and  Disadvantages  of  Inclined  Elevators 313,  315 

CHAPTER  XXIII.     ELEVATOR  CASINGS 

Forms  of  Sheet-steel  Casings 317 

Dust-tight  Casings 318 

Casings  for  Elevator  Heads 319 

Other  Forms  of  Belt  Elevators  . .                                                                                             .  320 


TABLES 

PAGE 

1.  Comparative  Resistance  of  Belts  to  Blows  and  Abrasion.. 28 

2.  Tests  of  Compounded  Rubber,  Breakiafe  Strength  and  Elongation 28 

3.  Weight  of  Frictioned  FabricTand  Rubber  Covers 41 

4.  Weight  of  Standard  Rubber  Belts 42 

5.  Weight  of  Stitched  Canvas  Belts 49 

6.  Weight  of  Balata  Belts 51 

7.  "  Wooster"  Solid-woven  Cotton  Belt 52 

8.  "  Scandinavia  "  Solid-woven  Cotton  Belt 52 

9.  Tests  of  Several  Belts  used  for  Package  Conveyors 53 

10.  Absorption  of  Water  by  Various  Kinds  of  Belts 56 

11.  Spacing  of  Belt  Conveyor  Idlers 70 

12.  Pulley  Sizes  and  Idler  Spacing,  Stitched  Canvas  Belts 71 

13.  Dimensions  of  Uniroll  Idlers  (Carrying  Idlers) 85 

14.  Dimensions  of  Unirpll  Idlers  (Return  Idlers) 85 

15.  Factors  for  Horse-power  Formula 97 

16.  Horse-power  of  Certain  Belt  Conveyors  by  Several  Rules 100 

17.  Horse-power  of  Empty  Belt  Conveyors 101 

18.  Horse-power  for  Materials  only 102,  103 

19.  Horse-power  to  Lift  Materials  on  Inclined  Conveyors 104,  105 

20.  Ratio  of  Belt  Tensions  for  Various  Conditions 109 

21.  Ratio  of  Belt  Tension  to  Horse-power  Pull 110 

22.  Pull  in  Belt  due  to  Angle  of  Slope  of  Conveyor 113 

23.  Width  of  Belt  According  to  Size  of  Material 114 

24.  Thickness  of  Belt  for  Proper  Troughing  on  Standard  Idlers 115 

25.  Comparison  of  Belt  Tensions  in  Tandem  Drives 122 

26.  Carrying  Capacity  of  Troughed  Belts 147 

27.  Capacities  of  Belts  at  Various  Ratings 149 

28.  Capacities  of  Grain  Belts  with  Concentrators 151 

29.  Maximum  Advisable  Speeds  for  Belt  Conveyors 153 

30.  Reduced  Speeds  for  Loading  on  Inclines 154 

31.  Ordinates  to  Lay  Out  Path  of  Discharge  over  Pulley 158 

32.  Causes  which  Shorten  the  Life  of  a  Belt 197 

33.  Actual  Life  of  Certain  Rubber  Conveyor  Belts 198 

34.  Comparative  Service  and  Cost  of  Certain  Belts 201 

35.  Head  Wheels  and  Speeds,  Centrifugal  Discharge  at  High  Speed 212 

36.  Head  Wheels  and  Speeds,  Centrifugal  Discharge  at  Moderate  Speed 216 

37.  Head  Wheels  and  Speeds,  Centrifugal  Discharge  at  Low  Speed 220 

38.  Carrying  Capacity  of  Grain  Elevator  Buckets 230 

39.  Malleable  Iron  Buckets,  Style  A 231 

40.  Malleable  Iron  Buckets,  Style  AA 232 

41.  Malleable  Iron  Buckets,  Style  B .233 

42.  Malleable  Iron  Buckets,  Style  C 233 

43.  Spacing  of  Buckets,  Free-flowing  Materials 234 

44.  Spacing  of  Buckets,  Coarse  Materials 234 

45.  Elevators  in  a  Concentrating  Works  in  New  Mexico 238 

46.  Relation  of  Height  of  Bucket  to  Diameter  of  Pulley 243 

47.  Dimensions  for  Two  Rows  of  Bolts 257 

48.  Bolt  Spacing  in  Sheet-steel  Buckets 259 

49.  Bolt  Spacing  in  Malleable-iron  Buckets 260 

50.  Variation  of  Coefficient  of  Belt  Friction 267 

51.  Effect  of  Dust  and  Dirt  on  Belt  Contact 268 

52.  Calculation  of  Elevator  Belt  Stresses  and  Horse-powers 271 

53.  Work  of  Pick-up  in  Elevator  Boot 273 

54.  Minimum  Number  of  Plies  in  Elevator  Belts 275 

55.  Rim  Thickness  of  Standard  Double-belt  Pulleys 279 

56.  Artificial  Tension  for  Vertical  Belt  Elevators 299 

57.  Factors  for  Inclined  Belt  Elevators 308 

58.  Head  Wheels  and  Speeds,  Centrifugal  Discharge  at  Low  Speed 314 

xi 


BELT  CONVEYORS  AND  BELT  ELEVATORS 

SECTION  I.— BELT  CONVEYORS 


CHAPTER   I 
GENERAL  DESCRIPTION  OF  COMPONENT  PARTS 

A  belt  conveyor  consists  of  a  moving  endless  belt  which  supports  material 
and  which  by  its  motion  carries  the  material  from  one  place  to  another. 
The  belt  is  driven  by  a  pulley,  and  is  supported  on  both  runs,  going  and 
coming,  by  rollers  or  by  a  runway.  The  material  may  be  put  on  the  belt 
by  hand,  shovel,  chute  or  some  other  means,  and  it  is  removed  from  the 
belt  by  discharging  it  over  the  end  pulley  or  by  deflecting  it  at  some  point 
along  the  run  of  the  conveyor. 

The  elements  of  a  belt  conveyor  are,  therefore : 

1.  A  belt  to  carry  the  material  and  transmit  the  pull. 

2.  Means  to  support  the  belt,  usually  rollers  or  pulleys. 

3.  Means  to  drive  the  belt,  usually  a  pulley  or  a  pair  of  pulleys. 

4.  (a)  Accessories  for  maintaining  belt  tension,  such  as  take-ups. 
(6)  Accessories  for  loading  the  belt,  such  as  a  chute. 

(c)  Accessories  for  discharging  the  material,  such  as  a  chute  or  a 
tripper. 

(d)  Accessories  for  cleaning  and  protecting  the  belt,  such   as  hous- 
ings, decks,  covers,  cleaning  brushes,  etc. 

The  belt  is  a  flexible  jointless  structure  which  runs  quietly  at  any  speed; 
it  is  not  ordinarily  harmed  by  the  actual  conveying  of  the  material  it 
carries.  Since  the  material  does  not  come  into  contact  with  the  moving 
surfaces  of  pulleys  and  shafts  in  which  there  are  friction  losses,  these  losses 
are  relatively  small  and  the  power  required  for  the  transfer  of  material  is 
generally  less  than  in  other  forms  of  conveyors.  The  belt  with  its  rollers 
weighs  less  per  foot  of  run  than  other  types  of  conveyors  doing  the  same 
or  similar  work,  and  hence  frames,  bridges  and  other  supporting  structures 
are  relatively  lighter  and  cheaper. 

Belt  conveyors  are  suited  to  the  carrying  of  all  sorts  of  material,  wet  or 
dry,  from  the  lightest  to  the  heaviest,  and  in  any  quantity.  They  have 
been  known  and  used  for  over  a  hundred  years,  but  the  most  rapid  develop- 
ment in  their  design  and  use  has  occurred  since  1893. 


2  GEN^RAk  QBSCiUmoX-QF  COMPONENT  PARTS 

The  Belt. — The  belt  must  have  a  certain  flexibility  in  order  to  wrap 
around  the  pulleys,  width  enough  to  carry  the  required  quantity  of  material 
and  strength  enough  to  bear  the  weight  of  the  load  and  transmit  the  pull  in 
the  conveyor.  These  conditions  can  be  met  by  bands  of  metal,  leather,  or 
woven  fabric.  For  metal  belts  see  page  60.  Leather  belts  are  expensive 
and  do  not  resist  wet  and  abrasion  well  enough  in  conveyors  and  elevators 
to  justify  their  greater  cost. 

Belts  of  hemp  fiber  are  used  to  some  extent  in  Europe,  but  in  this 
country  practically  all  conveyor  and  elevator  belts  are  made  of  cotton 
fiber.  They  are  of  several  forms : 

1.  Rubber  belts  are  made  of  layers  or  plies  of  cotton  duck  cemented 
together  by  an  elastic  rubber  compound.     In  "  friction  surface  "   belts  the 
outside  of  the  belt  is  covered  by  the  thin  layer  of  compound  adhering  to  the 
outer  plies;   in  rubber-covered  belts  an  extra  layer  of  rubber  compound  is 
attached  to  the  outer  plies  beyond  the  thin  coating  of  "  friction  rubber." 
No  attempt  is  made  to  waterproof  the  individual  cotton  fibers,  the  layers 
of  rubber  being  depended  upon  to  keep  moisture  out  of  the  belt.     See 
page  20. 

2.  Stitched  canvas  belts  are  made  of  layers  or  plies  of  cotton  duck 
folded  together  to  give  the  required  width  and  thickness,  and  then  sewed 
through  and  through  with  strong  cotton  twine.     To  waterproof  the  fibers 
and  to  reduce  internal  wear,  the  made-up  belt  is  impregnated  with  a  mix- 
ture of  oil  and  gum.     See  page  46. 

3.  Balata  belts  are  made  of  duck  with  the  fibers  of  the  cotton  water- 
proofed by  impregnation  with  a  liquid  solution  of  balata,  a  tree-gum  similar 
in  some  ways  to  rubber.     The  impregnated  duck  is  folded  and  rolled  under 
pressure  to  make  a  belt  of  the  required  width  and  thickness,  the   balata 
gum  acting  as  a  cement  to  hold  the  plies  together.     See  page  49. 

4.  Solid-woven  belts  consist  of  a  number  of  layers  of  warp  (lengthwise) 
threads  and  weft  or  filler  (crosswise)  threads  woven  and  interbound  together 
in  a  loom  to  make  a  structure  of  fabric  of  the  necessary  width  and  thick- 
ness.    Most  of  them  are  waterproofed  like  stitched  canvas  belts,  but  some 
are  impregnated  with  a  rubber  solution  and  then  covered  with  a  rubber 
sheathing.     See  page  50. 

Supports  for  the  Belt. — Supporting  idlers  consist  of  rollers  or  pulleys,  of 
wood,  cast  iron  or  steel  in  various  forms  and  combinations.  For  light 
work,  especially  in  handling  packages,  the  roller  may  be  a  cylinder  of  hard 
wood  (Fig.  1),  or  a  piece  of  thin  steel  tubing  with  inserted  heads  of  wood  or 
metal  (Fig.  2).  For  heavier  work,  the  roller  may  consist  of  several  cast- 
iron  pulleys  mounted  on  a  through  shaft  (Fig.  3),  or  the  outer  pulleys  of  the 
combination  may  be  enlarged  at  their  outside  ends  (flared  idlers)  in  order 
to  lift  the  edges  of  the  belt  slightly  and  prevent  spilling  (Fig.  4).  When  it  is 
desired  to  increase  the  carrying  capacity  of  a  belt  it  may  be  bent  into 
trough  form  by  turning  up  the  edges  of  the  belt  by  troughing  or  "  concen- 
trator "  pulleys  (Fig.  5),  or  by  supporting  the  whole  width  of  the  belt 
on  idlers  in  which  two,  three,  four  or  five  pulleys  are  set  at  various 


DRIVING  THE  BELT 


and    bearings    and    driven 
a   source  of   power  through 


iiiiii 


angles  from  the  horizontal  to  trough  the  cross  section  of  the  belt  (Figs 
6,  7,  8,  9).. 

Driving  the  Belt. — The  drive 
for  a  belt  conveyor  consists  of  one, 
or  two  pulleys  around  which  the 
belt  wraps,  suitably  mounted  on 
shafts 
from 

belts,  chains,  gears,  or  other  means 
of  power  transmission.  The  sim- 
plest drive  is  that  in  which  the  belt 
wraps  half  way  round  the  end 
pulley;  this  is  usually  at  the  head 
end  or  delivery  end  of  the  conveyor 
toward  which  the  material  moves, 
but  it  may  be  at  the  foot  or  load- 
ing end  of  the  conveyor  (Fig.  10). 
If  180°  of  belt  wrap  is  not  enough 
to  drive  the  conveyor,  it  may  be 
necessary  to  get  a  greater  wrap  on 
the  driving  pulley  by  the  use  of 
a  snub  or  reverse-bend  pulley 
(Fig.  11).  For  still  greater  driving 
contact,  the  belt  may  be  led  around 
two  pulleys,  both  of  which  are 
drivers.  Figs.  12  and  14  show  two 
arrangements  of  these  tandem- 
drive  pulleys.  To  accomplish  the 
same  result,  a  pressure-belt  (Fig. 
13)  may  be  used  to  increase  the 
grip  between  a  conveyor  belt  and 
a  single  drive  pulley. 

Belt-conveyor  Accessories.  — 
Conveyor  belts  in  service  stretch 
more  or  less,  and  it  is  necessary 
to  have  means  to  "  take  up  "  or 
remove  the  slack  as  it  is  formed. 
At  some  point  in  the  conveyor,  a 
pulley  is  mounted  on  a  shaft  run- 
ning in  bearings  which  are  adjust- 
able in  position  either  by  a  screw 
or  by  a  weight.  Fig.  10  shows  a 
conveyor  with  a  screw  take-up  at 
the  head  end;  in  this  case  the  ten- 
sion required  to  pull  the  loaded  side  of  the  belt  is  transmitted  through  the 
take-up;  the  usual  position  for  the  take-up  is  at  the  foot  end  as  in  Fig.  11, 


FIGS.   1-9.— Supporting  Idlers  for  Loaded 
Run  of  Conveyor  Belts. 


4  GENERAL  DESCRIPTION  OF  COMPONENT  PARTS 

where  the  belt  is  under  less  tension.  In  Fig.  14  the  take-up  is  at  the  point 
of  least  tension,  that  is,  where  the  belt  runs  off  from  the  driver.  Fig.  12 
shows  a  take-up  shaft  with  a  pull-back  weight;  in  Fig.  17  a  "gravity" 


Fig.lO 


Plain  Drive  at  Foot,    Screw  Take-up  at  Head 
Load  by  a  Chute,   Discharge  by  Plow 
or  over  Head  Puller 


Fig.ll 

Snub -Pulley  Drive  at  Head  of  Horizontal  Run 
Screw  Take-up  at  Foot  of  Incline 


Load  by  Reciprocating  Plate  Feeder 

Discharge  at  Fized  Tripper  or  Over  Head  Pulley 


Fig.12 


Fig.13 


Tandem  Pulley  Drive 
anywhere  on  Return  Run 
Weighted  Take-up  at  Foot 
Load  by  Roll  Feeder 
Discharge  over  Head  Pulley 


Drive  with  Pressure  Belt  & 
Pulley  on  Return  Run      . 
Screw  Take-up  at  Foot    /J-, 
Load  by  Apron  Feeder 
Discharge  by  Movable  Tripper 


Fig.14 


Fig.15 


"  D O- 

Tandem  Pulley  Drive  at  Head 

Screw  Take-up  Next  to  Drive 

Load  from  Bin  by  Series  of  Chutes,  Fixed  or  Hinged 

Discharge  Over  Head  Pulley  -  Belt  Curves  from 

Horizontal  Run  into  Incline 


Snub  Drive  at  Head 

Sorew  Take-cp  at  Foot 

Load  from  Bin  by  a  Traveling  Chute 

Discharge  from  Horizontal  Run  over  Bend  Pulley  to  Incline! 

Run,  Lu«t  Discharge  at  Head  of  Incline 


Fig.16 


Fig.17 


Plain  Drive  at  Head 

Screw  Take-up  at  Foot .  Foot  Depressed 

Load  by  Chute 

Discharge  by  Automatic  Self-Reversing  Tripper 


Snub  Drive  at  Head 

•Weighted  Vertical  Take-up  «n  Return  Run 
Load  by  other  Conveyors  Through  Hinged  Chutes 
Discharge  Over  Head  Pulley 


Fig.19 


Shuttle  Conveyor  on  a  Wheeled  Frame 
Belt  Travel  is  Reversible,  Drive  Either  End 
Load  by  '-'-Way  Chute,  Discharge  over 
Either  End  for  Distance   Covered  by  the 
Travel  of  the  Frame 


•   lakc-up  at . 
Load  by  Chute,   Discharge  by  Fixed  Trippers  or  OTer 
Head  Pulley  to  a  Series  of  Bins  or  Tanks 


FIGS.  10-19. — Typical  Belt  Conveyors  with  Various  Arrangements  of  Drive,  Feed,  Dis- 
charge and  Take-up. 


take-up  on  the  return  belt  takes  care  of  the  slack  and  maintains  driving 
contact  on  the  end  pulley. 

Loading. — Loading  chutes  may  be  used  in  connection  with  a  gate  con- 
trolled by  hand,  as  in  drawing  grain  from  bins,  or  to  deliver  to  the  belt  a 


DISCHARGING  5 

supply  of  material  at  a  uniform  rate  as  in  Figs.  10  and  14.  .If  the  material 
is  hard  to  control  by  a  gate,  or  if  the  supply  is  intermittent  or  irregular, 
feeders  of  various  kinds  (Figs.  11,  12,  J.3)  are  used  in  connection  with  loading 
chutes. 

Discharging. — The  simplest  discharge  is  over  the  end  pulley  (Figs.  12, 
17) ;  sometimes  a  chute  may  be  required  there,  often  it  is  not.  If  the  dis- 
charge is  to  be  at  some  point  short  of  the  end  of  the  conveyor,  the  material 
may  be  deflected  sideways  from  the  conveyor  by  a  plow  or  scraper  set  diag- 
onally across  the  belt  (Fig.  10) ;  more  frequently  this  is  done  by  inverting 
the  belt  or  running  it  in  S  form  through  a  tripper  (Figs.  11,  12,  16,  19). 
In  the  tripper  or  "  throw-off,"  as  it  is  called  in  England,  the  material  leaves 
the  belt  as  it  reaches  the  top  of  the  upper  pulley  and  is  caught  in  a  chute 
which  directs  it  to  one  side,  or  by  means  of  a  by-pass  gate,  back  on  the  belt 
again  if  the  material  is  to  be  carried  past  the  tripper  as  in  Figs.  11  and  19. 
Trippers  may  be  fixed  (Fig.  10),  or  movable  (Fig.  13),  or  traveling  and  self- 
reversing  (Fig.  16),  and  may  be  operated  by  hand  or  power. 

Protecting  the  Belt.— The  belt  is  the  most  expensive  part  of  a  belt  con- 
veyor, often  costing  more  than  all  the  rest  of  the  machinery  and  accessories 
combined.  At  the  same  time  it  is  the  most  vulnerable  part;  it  is  subject 
to  abrasion  from  impact  of  the  material  and  to  a  number  of  injuries  from 
negligence  or  accident.  Injury  at  the  loading  point  can  be  avoided  by 
proper  design  of  the  chute;  other  mishaps  can  be  prevented  by  care  in 
operation  and  maintenance.  To  lessen  the  risk  of  certain  other  injuries  it  is 
necessary  to  provide  means  to  clean  the  belt  from  adhering  particles,  to  cover 
it  where  it  is  exposed  to  the  weather,  and  to  prevent  it  from  being  cut  by 
objects  falling  against  it  or  upon  it. 


CHAPTER   II 


DEVELOPMENT  OF  BELT  CONVEYORS 


History  in  the  United  States. — The  earliest  reference  to  the  use  of  belt 
conveyors  in  American  practice  is  in  Oliver  Evans'  "  Miller's  Guide  "  published 
in  Philadelphia  in  1795.  This  describes  and  illustrates  a  flat  belt  receiving 
material  on  its  upper  run  and  discharging  over  the  end;  Evans  calls  it  "  a 
broad  endless  strap  of  thin  pliant  leather  or  canvas  revolving  over  two  pulleys 
in  a  case  or  trough."  In  the  flour  and  grist  mills  built  by  Evans  and  his  suc- 
cessors some  of  these  conveyors  were  probably  used,  but  it  was  more  common 
in  those  days  to  use  screw  conveyors  to  convey  grain  as  well  as  the  lighter 
mill  products. 

Belts  sliding  in  troughs  (Fig.  20)  were  used  before  1840  to  convey  materials 
which  were  not  suitable  for  screw  conveyors,  such  as  clay,  shavings,  saw-mill 


\S) 


FIG.  20. — Conveyor  Belt  Sliding 
in  Wood  Trough,  1830. 


FIG.  21. — Clay  Conveyor  Belt  Sup- 
ported on  Rollers,  1870. 


refuse  and  crushed  stone.  Sometimes  the  return  run  slid  back,  sometimes  it 
was  carried  on  rollers.  In  some  cases  the  sides  of  the  trough  were  made  with 
hinged  sections  which  swung  inward  to  stand  diagonally  across  the  belt  and 
thus  discharge  material  along  the  run  of  the  conveyor. 

When  such  conveyors  were  used  for  hard  and  gritty  substances,  the  belt 
did  not  last  long.  In  clay  conveyors,  the  clay  stuck  to  the  sides  and  bottom  of 
the  trough,  hardened  there,  and  wore  out  the  belt  rapidly.  Some  of  these 
troubles  were  avoided  in  the  design  shown  in  Fig.  21,  which  represents  a  form 
of  clay  conveyor  in  extensive  use  forty  years  ago.  This  construction  substituted 
rolling  friction  in  lubricated  bearings  for  sliding  friction  on  dirty  rough 
surfaces;  it  saved  power  and  helped  to  preserve  the  belt,  although  the 
material  could  not  be  carried  without  some  leakage  under  the  skirt-boards 
or  trough  sides,  and  the  edges  of  the  belt  were  still  subject  to  injurious  wear. 

The  great  increase  in  the  quantity  of  grain  handled  in  this  country  after 

6 


INVENTION  OF  THE  TRIPPER 


1850  and  the  development:  of  the  grain  "  elevator  "  or  storage  system 
created  a  demand  for  belts  of  larger  carrying  capacity.  Merrick  &  Sons, 
of  the  Southwark  Foundry  in  Philadelphia,  who  built  the  Washington 
Avenue  Grain  Elevator  there  between  1859  and  1863,  used  wide  composite 
belts  which  consisted  of  two^parallel  father  belts  to  which  at  intervals  were 
riveted  bent  iron  bars  or  spreaders  to  support  a  trough  of  canvas  which 
carried  the  grain.  This  construction  was  similar  to  Fig.  22;  power  was 
applied  to  the  edge  belts  by  iron  pulleys  separated  by  the  width  of  the 
canvas  trough,  or  by  a  wooden  drum  grooved  to  clear  the  sag  of  the  canvas. 
Narrow  pulleys  for  idlers  supported  the  edge  belts  on  the  loaded  run  and  on 
the  empty  run. 

Grain  conveyors  of  this  kind  were  installed  in  other  American  "  Ele- 
vators "  during  the  sixties.  As  used  at  Duluth  early  in  the  seventies  (T.  W. 
Hugo,  Transactions  A.  S.  M.  E.,  1884),  they  consisted  of  rubber  belts  7 
inches  wide  (Fig.  22)  supporting  a 
canvas  trough  2  feet  wide,  which 
sagged  4  or  5  inches  in  the  middle. 
They  ran  at  650  feet  per  minute  and 
carried  12,000  bushels  of  wheat  per 
hour.  A  composite  belt  of  this  kind 
had  only  12  or  14  inches  of  belt 
width  to  engage  the  face  of  the 
driving  pulley  and  hence  the  length 
of  the  conveyor  was  limited  to  what 
that  width  of  pulley  face  would 


FIG.  22. — Composite  Belt  for  Grain 
Conveyor,  1870. 


drive,  but  on  the  other  hand,  the 

load    to    be    pulled     corresponded 

to  that  of  a  belt  24  inches  or  more  in  width.     Aside  from  that  disadvantage 

the  edge  belts  would  not  stretch  alike,  the  spreader-bars  would  tear  loose 

from  their  fastenings,  and  when  the  bars  pulled  loose,  the  belts  came  off  the 

idlers  and  there  was  serious  trouble. 

Invention  of  the  Tripper. — On  February  10th,  1863,  United  States  patent 
37615  was  issued  to  Oren  C.  Dodge  of  New  York  with  the  following  claims: 

1.  "  Delivering  the  grain  at  any  desired  point  along  the  line  of  a  traveling 
belt  by  bending  such  belt  substantially  as  specified,  for  the  introduction  of  a 
hopper  or  chute. 

2.  "  A  traveling  belt  for  conveying  grain,  provided  with  vertical  or  nearly 
vertical  edges,  forming  a  trough." 

Dodge's  drawings  show  an  arrangement  of  fixed  trippers  and  a  belt  with 
low  upstanding  flanges  and  supported  on  cylindrical  rollers. 

Grain  Conveyors  at  Liverpool. — About  1865,  P.  G.  B.  Westmacott  and 
G.  F.  Lyster,  engineers  for  the  Birkenhead  and  Waterloo  Docks  at  Liverpool, 
England,  made  experiments  with  a  12-inch  belt  which  showed  that  belt 
conveyors  carried  more  grain  with  less  power  than  screw  conveyors.  In 
1866  they  installed  a  system  consisting  of  a  skip  hoist  for  elevating  the  grain 
with  belts  for  distributing  it.  The  belts  were  18-inch  2-ply  rubber,  run  at 


8 


DEVELOPMENT  OF  BELT  CONVEYORS 


450  to  500  feet  per  minute  and  supported  every  6  feet  on  straight  wooden 
rolls.  Discharge  was  effected  by  running  the  belt  through  a  traveling  tripper 
pushed  by  hand.  Tuck-up  or  concentrator  rolls  mounted  on  portable  frames 
were  used  to  keep  the  grain  back  from  the  edge  of  the  belt  at  the  loading  point 
and  where  the  belt  began  to  lift  into  the  tripper.  How  much  Westmacott 
and  Lyster  knew  about  American  practice  at  that  time  we  cannot  say.  West- 
macott's  account  of  their  work  (Proceedings  Inst.  of  Mech.  Engrs.,  1869) 
makes  no  reference  to  the  prior  use  of  belts  for  grain  in  the  United  States  nor 
to  the  use  of  trippers  there.  The  traveling  tripper  was  covered  by  Westma- 
cott's  British  patent  No.  3061  of  1866,  and  U.  S.  patent  No.  66759,  in  1867; 
it  was  new  and  was  a  great  improvement  over  the  fixed  trippers  shown  in  the 
Dodge  patent. 

Development  of  Grain  Conveying. — The  improvements  made  at  Liver- 
pool were  taken  up  by  American  engineers,  at  first  by  W.  B.  Reaney  in 
alterations  at  the  Washington  Avenue  Elevator  in  1873  and  in  the  design 
of  a  complete  new  Elevator  (Canton  No.  1)  for  the  Northern  Central  Rail- 
road at  Baltimore  in  1876.  In  this  Elevator,  designed  by  Reaney  and  built 
by  John  T.  Moulton  &  Son  of  Chicago,  the  conveyor  belts  were  30  inches 
wide  4-ply  rubber  and  ran  at  550  feet  per  minute  over  straight  wood  rolls 
placed  every  5  feet  on  the  carry  and  10  feet  on  the  return.  Wooden  con- 
centrator pulleys  similar  to  Fig.  23  were  used  at  the  loading  points  only. 
This  work  by  Reaney  introduced  wide  rubber  belts  into  the  business  of 
handling  grain.  For  a  reference  to  a  rubber  belt  which  he  installed  at 
Philadelphia  in  1873,  see  page  30. 

The  Canton  No.  1  Elevator  had  the  first  traveling  trippers  in  which  the 
moving  power  was  taken  from  the  conveyor  belt. 

In  other  grain  conveyors  built  in  this  country  up  to  1885,  the  belts  were 
made  to  give  greater  capacity  by  troughing 
them  over  spool-shaped  idlers  (Fig.  23).  As 
long  as  the  difference  between  the  middle  and 
end  diameters  was  only  an  inch  or  two,  the 
pulley  side  of  the  belt  did  not  suffer  appre- 
ciably from  the  fact  that  the  edge  of  the 
idler  traveled  more  than  the  middle  in  feet 
per  minute  and  hence  must  rub  the  belt. 
When  the  trough  was  made  deeper  by  making 
the  sag  of  the  belt  2  or  2£  inches  (see  T.  W. 
Hugo's  paper),  the  wear  on  the  belt  was  great 
enough  to  be  noticed;  but  the  main  objection  to 
the  deep  spool  idler  as  used  on  some  grain  con- 
veyors was  that  a  belt  lightly  loaded  or 
empty  was  apt  to  run  crooked.  This  trouble 

always  exists  where  all  or  a  great  part  of  the  weight  of  belt  and  load 
is  carried  on  revolving  conical  surfaces  or  on  separate  cylindrical  surfaces 
which  are  set  to  trough  the  belt,  (see  page  77).  It  led  first  to  the  use  of  guide 
pulleys  to  bear  against  the  edge  of  the  belt,  always  a  dangerous  and  destruc- 


Kod  with  B  and  L  Threads 
One  End  Squared  for  Crank' 

Nut  with  Stop. 

FIG.  23. — Carrying  Idler  and 
Concentrator  Roll  36-inch 
Grain  Belt.  (John  T.  Moul- 
ton &  Son,  1880.) 


DEVELOPMENT  OF  GRAIN  CONVEYING 


9 


tive  thing;  then  to  the  use  of  the  "  dish-pan  "  idler  which  came  into  use  in 
the  late  seventies  (Fig.  24).  By  having  the  end  rolls  or  "  dish-pan  "  loose 
on  the  shaft  and  free  to  turn  independently  of  the  horizontal  pulley,  there 

was  less  chafing  of  the  belt 
than  with  deep  spool  idlers 
as  long  as  the  belt  had  a 
slight  contact  with  the  end 
rolls  (Fig.  24,  left  half). 
Under  a  heavy  load,  how- 
ever, the  belt  assumes  the 
shape  shown  in  Fig.  24,  right 


FIG.  24. —  "Dish-pan  "  Idler  and  Return  Idler  for 
36-inch  Grain  Belt,  1880. 


half,  and  the  pulley  side  is 
rubbed  so  as  to  cause  a 
noticeable  loss  of  power  in 
driving  the  conveyor.  Besides  that,  there  was  difficulty  in  making  the  belt 
run  straight  in  the  narrower  widths,  and  after  1890  this  form  of  idler  gradually 
became  obsolete. 

After  twenty  years  of  experience  with  various  kinds  of  belt  idlers, 
designers  of  grain-elevator  equipment  in  this  country  reached  the  conclusion 
that  the  right  way  to  convey  grain  is  by  a  belt  that  is  flat  (Fig.  25)  or 


FIG.  25. — 40-inch  Flat  Grain  Belt,  1897.     (Link-Belt  Company.) 

nearly  so.  A  flat  belt  has  a  good  contact  with  the  horizontal  idler  pulleys 
and  will  run  straight,  empty  or  loaded,  or  even  loaded  to  one  side  of  the 
center.  Grain  carefully  fed  to  a  flat  belt  will  not  tend  to  shift  toward  the 
edges  and  spill  (see  Fig.  140),  but  to  prevent  scatter  at  the  loading  points 
and  to  increase  the  carrying  capacity  moderately  it  is  customary  to  use 
inclined  concentrator  pulleys  at  the  loading  points  only,  or  at  intervals 
along  the  length  of  the  conveyor  (Fig.  26).  The  first  concentrators  used 
in  this  country  were  inclined  at  60°  (Fig.  23),  but  as  many  cases  of  longi- 
tudinal cracking  of  belts  could  be  proved  against  the  severe  bend  in  the  belt, 


10 


DEVELOPMENT  OF  BELT  CONVEYORS 


the  angle  was  reduced  to  45°,  and  then  to  35°,  which  is  now  most  common. 
Concentrators  with  angles  of  30°  and  22°  are  also  made,  to  reduce  still 
further  the  flexure  of  the  edges  of  the  belt. 

In  modern  practice  the  concentrators  may  be  used  on  a  separate  stand 


FIG.  26. — 36-inch  Grain  Belts  with  Concentrators  every  15  Feet. 
(James  Stewart  &  Co.,  1908.) 

(Fig.  27)  or  combined  with  the  horizontal  pulleys  (Fig.  28),  or  a  stand  may 
be  used  to  take  the  return  idlers  also. 

Conveying  Materials  Heavier  than  Grain. — With  the  development  of 
conveying  machinery  between  1880  and  1890  belts  were  used  for  handling 


FIG.  27. — Concentrator  Pulleys  Mounted  on  a  Separate  Stand. 

coal,  ore  and  other  materials  heavier  than  grain.  Designers  followed  grain 
elevator  practice  as  to  belts  and  idlers.  One  of  the  largest  installations  in  the 
early  nineties  was  the  ore  concentrating  plant  of  the  New  Jersey  and  Penn- 
sylvania Concentrating  Co.  at  Edison,  N.  J.  It  had  over  50  belt  conveyors, 
ranging  from  20  inches  to  30  inches  wide  and  up  to  500  feet  long.  The 


IMPROVEMENTS  BY  THOMAS  ROBINS 


11 


first  idlers  used  there  about  1891  were  heavy  cast-iron  spool  idlers,  but 
these  were  failures  because  in  order  to  get  the  greatest  capacity  from  the 
belts,  the  troughing  was  deep  and  the  spools  were  much  larger  at  the  ends 
than  at  the  middle.  These  were* heavier  than  the  spools  used  on  grain 
conveyors;  the  work  was  continuous,  the  place  dusty,  and  the  belts  wore 


FIG.  28. — Concentrators  Mounted  on  a  Stand  with  Carrying  Pulleys. 

out  rapidly.  When  the  plant  was  rebuilt  in  1893  idlers  of  the  type  shown  in 
Fig.  29  replaced  the  spool  idlers;  the  new  idlers  were  practically  the  same 
as  the  flat  rolls  with  concentrators  used  on  grain  conveyors. 

The  chief  trouble  at  Edison  and  at  other  places  doing  similar  work  was 
with  the  belts.  The  sharp  pieces  of  heavy  ore  cut  the  fabric  and  the  stitching 
of  canvas  belts  and  loosened  the  plies;  the  same  thing  happened  with  rubber 


FIG.  29.— Troughing  Idler  for  Ore  Conveyor.     (Edison,  N.  J.,  1893.) 

belts.  We  know  now  that  much  of  the  difficulty  was  due  to  improper 
delivery  of  material  to  the  belts  and  to  improper  construction  of  the  belts 
themselves.  Fig.  30  shows  a  transfer  between  two  belts  at  Edison;  appar- 
ently no  attempt  was  made  to  deliver  material  to  the  receiving  belt  with  some 
velocity  in  the  direction  of  travel. 

Improvements  by  Thomas  Robins. — Thomas  Robins,  Jr.,  then  in  the 
business  of  making  rubber  belts,  visited  the  plant  about  1891  and  noticed 
the  following  points:  1,  that  the  thin  layer  of  rubber  which  covered  the  belt 


12 


DEVELOPMENT  OF  BELT  CONVEYORS 


resisted  abrasion  much  longer  than  did  the  duck  which  formed  the  body  of 
the  belt;  2,  that  each  layer  of  duck  wore  out  faster  than  the  one  preceding 
it,  showing  that  as  the  belt  wore  thin  and  the  tension  on  the  threads  increased 
they  were  cut  more  easily;  3,  that  belts  wore  out  in  the  middle  and  split 
longitudinally  while  the  edges  were  still  good  (Trans.  A.  I.  M.  E.,  April, 
1896).  From  these  observations  Mr.  Robins  concluded  that  the  sole  func- 
tion of  the  fabric  in  a  rubber  belt  should  be  to  give  the  belt  tensile  strength 
and  that  it  should  be  protected  from  injury  by  a  cover  of  rubber  compound 
that  would  resist  abrasion  better  than  the  cotton  threads  or  the  thin  layer 


FIG.  30. — Transfer  of  Ore  between  Two 
Belts.     (Edison,  N.  J.,  1893.) 


FIG.  31. — Original  Robins'  Belt  with  Extra 
Thickness  of  Rubber  in  Center,  1893. 


of  friction  rubber  that  covered  them.  After  experiments  with  various  rubber 
compounds,  he  furnished  belts  with  a  thick  face  of  rubber  that  proved  to  be 
much  more  durable  than  those  previously  used,  lasting  years  where  others 
lasted  months.  In  1893  he  patented  the  belt  shown  in  Fig.  31,  which  has  an 
extra  thickness  of  rubber  at  the  center  to  resist  the  abrasion  which  comes 
from  feeding  material  from  a  comparatively  narrow  chute;  it  resisted 
abrasion  very  well  but  the  belt  was  so  stiff  that  it  would  not  conform  to  the 
shape  of  the  troughing  idlers,  which,  as  shown  in  Fig.  29,  had  the  side  pulleys 
inclined  at  45°. 

In  1896  Mr.  Robins  patented  his  "  stepped-ply  "  belt  (Fig.  32)  in  which 


FIG.  32.— Robins'  Stepped-ply  Belt,  1896. 

the  belt  thickness  is  the  same  for  the  entire  width  but  the  plies  of  fabric  are 
fewer  at  the  middle  than  at  the  edges.  The  space  left  by  the  omission  of  the 
plies  was  filled  with  the  rubber  of  the  top  cover,  making  the  extra  thickness 
of  protective  cover  there  equivalent  to  that  shown  in  Fig.  31,  but  using  less 
rubber  where  the  abrasion  was  not  so  great.  The  omission  of  the  plies 
at  the  middle  made  the  belt  more  flexible  in  cross  section,  allowed  it  to 


IMPROVEMENTS  BY  THOMAS  ROBINS 


13 


conform  more  closely  to  the 'shape  of  the  troughing  idlers  and  at  the  same 
time  left  a  thick  stiff  edge  to  bear  against  the  side  guide  pulleys  (P',  Fig.  33). 
These  pulleys  were  necessary  to  keep  the  belt  straight  on  45°  troughing 
idlers,  especially  when  the  belts  were  comparatively  narrow  and  stiff  and 
when  the  inclined  idlers  came  every 
4  or  5  feet.  Idlers  inclined  at  45° 
were  in  successful  use  on  grain  con- 
veyors, but  there  the  belts  were 
relatively  wide  and  thin  and  the 
troughing  occurred  only  at  the  load- 
ing points  or  at  intervals  not  closer 
than  8  or  10  feet.  Under  these 
conditions  the  grain  belt  had  a  good 
guiding  contact  with  the  horizontal 
pulleys  and  did  not  usually  require 
side  guide  idlers  to  keep  it  straight; 
but  with  stiff  and  narrow  belts  on 
45°  idlers,  the  guiding  contact  on 
the  horizontal  pulleys  was  slight,  the 
side  guide  pulleys  were  necessary 


FIG.  33. — Stepped-ply  Belt  on  45°  Trough- 
ing Idlers  with  Side-guide  Pulleys,  1896. 


and  the  belt  had   to    have  a  thick 

stiff  edge;   otherwise  the  edges  were  chafed,  bent  over  or  rubbed  off  and 

the  belt  destroyed. 

In  the  early  days  of  the  belt-conveyor  business,  say  before  1900,  compara- 
tively few  belts  wider  than  24  inches  were  used.  Troughing  was  considered 
a  means  to  permit  a  narrow  belt  to  carry  what  would  otherwise  require  a 
wider  and  more  costly  belt,  and  the  tendency  was  to  use  belts  narrower  than 
would  now  be  considered  good  practice. 

The  Robins  patent  (571604,  Nov.  17,  1896)  covers  also  the  idler  con- 
struction shown  in  Fig.  34,  with  the  following  claims:  "  Claim  5.  The 

supporting  pulleys  L,  K,  L,  the  hollow 
bearings  F,  therefor,  and  the  horizontal 
and  turn-up  hollow-shafts  secured  in 
the   said  bearings,  and  the  oil  devices 
mounted  on    the  ends  of  the  turn-up 
shafts,    substantially    as    set     forth." 
"  Claim   6.    In   combination    the   two 
brackets  or  castings  suitably  supported, 
the    horizontal    pulley    mounted    be- 
tween them,  the  turn-up  shafts  secured 
and    the    pulleys    L   loosely    turning 
This  idler  followed  earlier  designs 
45°   (Trans.   A.   I.  M.  E., 


FIG.  34. — Robins'  Three-pulley  Idler, 
1896. 


in    the   said    brackets    or    castings 

thereon,  substantially  as  set  forth." 

in   having   the   troughing   pulleys   inclined   at 

April,  1896),  but  it  differed  from  them  in  combining  the  troughing  idler  group 

into  one  self-contained  unit  by  using  only  two  castings  to  support  the 

pulley  shafts  instead  of  four  (compare  Figs.  34  and  29).     This  arrangement 


14  DEVELOPMENT  OF  BELT  CONVEYORS 

with  pulleys  turning  loose  on  hollow  shafts  permitted  lubrication  from  two 
points  instead  of  .four,  and  at  the  same  time  the  idler  itself  was  easier  to 
install  and  to  use;  there  was  no  distinction  between  front  and  back  as  in 
the  older  form  where  the  belt  ran  on  to  the  horizontal  pulley  first  (see  Fig.  29). 
Although  the  figure  in  the  patent  shows  the  three  pulleys  in  a  single  plane, 
that  feature  is  not  referred  to  in  the  language  or  the  claims  of  the  patent; 
it  seems  to  have  been  adopted  as  a  means  of  effecting  lubrication  in  a  certain 
way. 

Prior  to  1890  much  had  been  done  toward  the  improvement  and  standard- 
ization of  grain  conveyors  by  John  T.  Moulton,  James  A.  Macdonald,  the 
Webster  &  Comstock  Mfg.  Co.  and  others  interested  in  the  grain  elevator 
business,  but  belt  conveyors  had  not  been  used  extensively  for  materials  other 
than  grain.  Mr.  Robins'  great  contribution  to  the  industry  was  an  active 
company  which  began  in  1896  to  design  and  sell  belt  conveyors  for  handling 
coal,  ores,  stone  and  all  similar  materials.  Before  that  time  most  of  the  busi- 
ness in  this  line  lay  between  the  belt  maker  and  the  pulley  maker,  neither  inter- 
ested in  the  other's  product  and  neither  capable  of  giving  engineering  advice 
nor  of  insuring  definite  results  from  the  operation  of  the  conveyor.  There 
was  a  great  expansion  in  the  use  of  all  kinds  of  conveying  machinery  between 
1895  and  1910  and  the  belt  conveyor  had  its  share  of  the  growth.  To  Mr. 
Robins  and  his  company  must  be  given  the  credit  for  most  of  the  pioneer  work 
in  extending  the  use  of  belt  conveyors  to  the  handling  of  materials  other  than 
grain  and  in  laying  the  foundations  for  the  engineering  knowledge  of  the  busi- 
ness. Others  entered  the  field,  some  with  devices  intended  to  evade  the  Robins 
patents,  others  with  improvements  suggested  by  the  growing  experience  of 
makers  and  users  of  belt  conveyors. 

Changes  in  Belt  and  Idler  Construction. — The  earliest  Robins  idlers 

had  a  rather  wide  gap  beween  the  adjacent 
edges  of  the  pulleys,  a  distance  sufficient  to 
allow  a  heavily  loaded  belt  or  an  old  limber 
belt  to  sag  between  the  pulleys,  as  shown  in 
Fig.  35.  The  same  defect  existed  in  various 
two-pulley  (Fig.  6),  four-pulley  (Fig.  8)  and 
tw°-Plane  three-pulley  idlers,  in  which  the 
edges  were  not  brought  close  together.  After 
the  first  few  years  of  experience,  the  gap  was  made  less,  and  in  the  majority 
of  modern  idlers,  the  distance  between  the  pulleys  is  made  as  small  as  prac- 
ticable, i.e.,  about  i  or  $  inch. 

Two-pulley  and  four-pulley  troughing  idlers  are  now  practically  obsolete. 
When  the  belt  sags  between  the  pulleys  of  a  troughing  idler  of  the  kind 
shown  in  Fig.  35,  it  is  not  only  in  danger  of  cracking  by  direct  flexure  under 
the  load,  but  there  is  a  tendency  of  the  edges  of  the  pulleys  to  seize  the  sag 
of  the  belt  and  squeeze  it  together  to  form  a  sharp  bend.  Comparing 
Figs.  36  and  37,  it  is  evident  that  the  greater  the  angle  at  which  the  pulleys 
are  inclined  to  each  other,  the  greater  is  the  wedge  angle  toward  which  the 
belt  travels  as  it  approaches  the  idler,  and  the  greater  the  chance  that  the 


CHANGES  IN  BELT  AND  IDLER  CONSTRUCTION 


15 


converging  edges  of  the  pulley  rims  will  seize  the  sag  of  belt  and  squeeze  it. 
This  squeezing  action  causes  the  belt  to  crack  or  to  split  lengthwise. 

From  examinations  of  spoiled  and  discarded  belts,  it  was  noticed  that 
splitting  was  more  apt  to  occur  if  the  longitudinal  joints  or  seams  in  one  or 
more  plies  of  duck  came  just  at  the&point  where  the  belt  was  bent  by  the 
troughing  pulleys,  or  if  that  line  of  flexure  in  a  stepped-ply  belt  happened 
to  come  where  the  thickness  of  the  plies  changed,  as  at  c,  Fig.  33.  In  early 
days  belt  makers  were  not  always  particular  as  to  how  the  duck  was  cut  and 
assembled.  If  the  width  was  made  up  of  several  narrow  strips  of  duck  and 


FIG.  36. 


FIG.  37. 


FIG.  36.— Angle  between  Pulleys  15°  Small  Wedge-angle. 

FIG.  37. — Angle  between  Pulleys  30°  Large  Wedge  Angle  and  Greater  Liability  to  Pinch 

the  Belt. 


if  the  butt-joints  where  the  edges  of  the  strips  met  came  at  the  same  place 
in  the  width  of  the  belt,  the  result  was  a  plane  of  weakness  which,  if  it  came 
just  at  the  place  where  the  belt  bent  for  troughing;  would  lead  to  the  destruc- 
tion of  the  belt.  As  a  result  of  knowledge  on  this  point,  belts  as  now  made 
by  careful  manufacturers  have  the  longitudinal  seams  or  joints  at  the  middle 
of  the  belt  or  near  its  edges  where  they  will  not  be  affected  by  the  bending  of 
the  belt  over  troughing  idlers  of  the  types  in  general  use. 

The  connection  between  the  steep  angle  of  troughing  and  the  splitting 
of  belts  was  quite  apparent  and  since  the  latter  was  a  serious  difficulty,  it 
was  not  long  before  the  angle  was  changed  by  Robins  and  others  from  45°  to 
35°,  while  later  idlers  were  made  with  the  angle 
30°,  25°,  20°  and  even  less.     These  changes 
helped  belts  in  still  another  way,  i.e.,  by  reduc- 
ing the  internal  stresses  in  the  belt  due  to  the 
shift  of   the  load  in   passing   over  the  idlers. 
In  Fig.  38,  A  represents  the  edge  of  the  load 
on  a  belt  troughed  at  45°.     Midway  between 
idlers,  the  edge    of  the  belt    drops    and  the 
load  slips  to  a  line  B;   this  readjustment  of 
the  load  extends   in  a  smaller  degree  to  the 

material  back  from  the  edge  of  the  belt;  some  of  it  is  on  the  surface  where 
it  can  be  seen,  but  some  of  it  is  within  the  cross-section  where  it  is  not 
noticed.  The  action  of  the  inclined  pulleys  in  pushing  back  the  load  is 


FIG.  38. — Disturbance  of  Load 
Cross-section  on  45°  Trough- 
ing Idlers. 


16  DEVELOPMENT  OF  BELT  CONVEYORS 

exerted  through  the  belt,  at  the  bend  it  produces  a  tensile  stress  on  the  filler 
(crosswise)  threads  in  the  fabric,  and  naturally,  the  less  the  angle  of  trough- 
ing  the  less  the  disturbance  of  the  load  and  the  less  the  stress  in  the  cross- 
wise threads  in  the  belt. 

On  the  loss  of  power  due  to  change  of  cross-section,  see  page  72. 

Belts  Running  Crooked. — It  was  a  common  experience  with  old-time 
belt  conveyors  that  the  belt  would  not  conform  well  to  the  contour  of  the 
45°  and  35°  troughing  idlers,  but  would  tend  to  lift  off  the  horizontal  pulley 
when  lightly  loaded  or  empty.  In  doing  this  the  belt  was  apt  to  be  cut  by 
the  edges  of  loading  chutes  and  skirt-boards  and  by  losing  the  guiding  effect 
of  the  horizontal  pulley,  the  belt  would  run  crooked.  As  has  been  stated, 
it  was  necessary  to  use  side-guide  idlers  to  keep  the  belts  centered  on  these 
idlers,  and  belts  were  often  damaged  by  the  constant  pressure  against  their 
edges.  A  later  chapter  explains  why  the  tendency  to  run  crooked  decreases 
as  the  angle  of  troughing  is  made  less.  This  connection  was  not  generally 
recognized  in  practice  but  it  is  a  fact  that  when  idlers  with  angles  of  30° 
and  less  came  into  use,  the  troubles  with  belts  running  off  center  became  less, 
there  was  less  need  for  side-guide  idlers  and  it  was  found  that  belts  of  uniform 
cross  section  (straight-ply  belts)  could  be  used  as  well  as  those  in  which 
greater  flexibility  and  better  contact  with  the  horizontal  pulley  were  attained 
by  omitting  plies  of  fabric  near  the  middle  of  the  belt  (stepped-ply  belts) . 

Multiple-pulley  Idlers. — Quite  early  in  the  belt-conveyor  business  there 
were  suggestions  that  if  idlers  were  made  with  more  than  three  pulleys  set 
to  maintain  the  same  depth  of  troughing  as  with  three-pulley  idlers,  the 
bending  action  on  the  belt  would  be  easier  and  the  conveyor  would  suffer  no 
loss  of  carrying  capacity.  By  the  use  of  a  greater  number  of  pulleys,  the 
belt  would  be  bent  through  a  smaller  angle  along  each  line  of  longitudinal 
flexure,  the  internal  stress  on  the  filler  threads  of  the  belt  fabric  would  be 
diminished,  there  would  be  less  risk  of  pinching  the  belt  between  pulleys 
and  the  tendency  to  crack  or  split  the  belt  would  be  less.  The  compli- 
cation of  parts  and  the  increased  difficulty  of  lubricating  the  pulleys  were 
obvious  disadvantages  which  delayed  the  introduction  of  multiple-pulley 
idlers  and  they  did  not  come  into  use  until  after  1905. 

The  first  United  States  patent  on  a  multiple-pulley  idler  was  that 
granted  to  Lynch  (1899)  which  shows  an  impractical  device  consisting  of  six 
pulleys  mounted  on  a  bent  shaft.  Plummer  in  1903  patented  a  five-pulley 
idler  like  those  now  in  use  except  that  the  faces  of  the  pulleys  were  concaved 
to  match  the  curve  of  the  belt  and  avoid  all  angular  bends.  Neither  of  these 
schemes  ever  came  into  practical  use. 

The  four-pulley  idler,  used  to  some  extent  fifteen  years  ago  (Fig.  8),  is  open 
to  the  objection  that  the  center  of  the  belt,  which  is  under  the  greatest  depth 
of  load,  is  apt  to  sag  between  the  middle  pulleys  and  be  rolled  into  the  gap 
and  split  along  its  whole  length.  The  Robins  idler  of  1909  (Fig.  39)  and  the 
Peck  idler  of  1913  are  alike  in  using  five  pulleys  with  the  inclined  pulleys  set 
at  15°  and  30°  from  the  horizontal.  Most  of  the  multiple-pulley  idlers  in  use 
at  the  present  time  are  made  with  this  arrangement  of  five  pulleys.  They  differ 


BELT  DEVICES  17 

chiefly  in  the  ways  of  making  and  assembling  the  cast-iron  brackets  that  support 
the  pulley  shafts. 

Expedients  to  Avoid  Cracking  pf  Belts. — The  splitting  of  belts  by 
longitudinal  cracks  was  a  serious  matter  in  the  early  days  of  the  belt  con- 
veyor business,  and  a  number  of  sdfeemes  were  brought  forward  to  .pre- 
vent it.  Some  of  these  referred  to  belt  construction,  others  to  idler  con- 
struction. Some  have  been  referred  to  on  previous  pages.  Of  those  named 
below,  not  one  is  in  commercial  use  to-day;  but  they  are  frequently  men- 
tioned, and  occasionally  some  similar  devices  are  newly  invented  and  brought 
to  the  notice  of  those  in  the  business. 

Belt  Devices. — The  Selleck  patent  of  1902  covers  a  conveyor  belt  com- 
posed of  a  central  strip  and  two  side  sections  flexibly  united  at  their  adjoining 
edges  by  interlocked  lacings,  the  lacings  being  coils  of  wire  enclosing  a 
flexible  thong  of  leather.  In  other  words,  the  inventor  starts  with  a  split 
belt  to  prevent  splitting.  Ridgway,  in  his  patent  of  1902,  omitted  some  of 
the  plies  at  the  bending  points  of  a  rubber  belt  and  increased  the  rubber 
there,  to  get  greater  flexibility.  Some  belts  of  this  "  hinged-edge  "  design 


Grease  cup  forces  | 


FIG.  39.— Robins'  5-pulley  Idler,  1909. 

were  used  in  this  country  and  in  England;  they  troughed  well  and  ran 
straight  and  in  some  cases  they  gave  satisfaction.  In  other  cases  the  belts 
showed  structural  weakness  along  the  lines  of  bend  owing  to  the  compara- 
tively few  filler  (crosswise)  threads  of  fabric  there.  In  other  words  these 
belts  were  half  split  to  begin  with;  the  bending  was  concentrated  along  the 
weak  lines  and  the  extra  rubber  could  not  hold  the  belt  together.  In  the 
three  Plummer  patents  of  1903  the  body  of  a  canvas  belt  is  made  thick  and 
impregnated  and  hardened  by  saturation  with  drying  oils,  while  the  wings 
are  made  of  fewer  plies,  and  being  treated  with  non-drying  oils,  remain 
flexible.  The  Ridgway  patent  of  1904  discloses  a  double  belt  structure  in 
which  the  load  is  carried  on  a  troughed  belt  which  is  supported  by  and 
receives  its  trough  shape  from  saddle-shaped  cleats  mounted  on  a  flat  belt 
running  underneath  over  its  own  separate  'pulleys.  This  scheme  was  costly 
and  complicated  and  did  not  get  beyond  the  stage  of  advertising  and  demon- 
stration. Plummer,  in  1906,  patented  a  canvas  belt  in  which  the  upper 
plies,  which  take  the  abrasion  of  the  material  carried,  are  stitched  together 
for  their  full  width,  but  fastened  to  the  lower  plies  at  their  longitudinal 
central  portions  only,  in  such  a  way  as  to  make  the  belt  flexible  for  troughing. 
This  belt  never  came  into  practical  use. 


18  DEVELOPMENT  OF  BELT  CONVEYORS 

Idler  Devices. — The  Mann  and  Neemes  idler  of  1902  consisted  of  a  spool 
idler  made  in  five  or  more  sections,  the  middle  section  tight  on  the  straight 
through-shaft,  the  outer  ones  loose.  It  was  intended  to  give  the  troughing 
of  a  deep  spool  idler  without  the  disadvantage  of  wear  on  the  under  side  of 
the  belt  (see  page  11).  It  would  do  this  if  each  loose  section  of  the  pulley 
were  sure  to  turn  freely  on  the  shaft,  but  since  lubrication  through  a  long 
hole  with  many  side  outlets  is  uncertain,  it  is  safe  to  say  that  some  of  the 
pulleys  would  not  turn  freely  and  the  belt  would  rub  and  run  crooked. 
Besides  that,  the  construction  is  apt  to  be  expensive  if  well  made.  The 
Rouse  idler  of  1907  represents  another  effort  in  the  same  direction.  Patents 
have  been  issued  at  various  times  since  1907  on  "  helical  "  idlers  in  which  the 
supporting  pulley  is  made  of  a  length  of  steel  rod  or  ribbon  wound  into  a 
helix  of  cylindrical  shape.  In  the  Thomas  idler  of  1907,  the  helix  forms  a 
tension  spring  that  bends  to  conform  to  the  weight  of  the  belt  and  its  load, 
the  ends  of  the  rod  being  extended  on  the  axis  of  the  helix  to  enter  ball- 
thrust  trunnion  bearings  carried  by  a  stand  at  each  side  of  the  conveyor. 
One  conveyor  equipped  with  these  idlers  was  set  up  in  Chicago;  when  a 
load  was  put  on  the  moving  belt  the  springs  vibrated  and  set  up  a  wave- 
motion  in  the  belt  which  made  it  inoperative.  Vrooman,  in  1909,  patented 
an  idler  of  similar  form  with  a  number  of  separate  pulleys  fitted  to  a  flexible- 
jointed  shaft  with  a  spring-mounted  end-thrust  bearing  at  each  side.  This 
had  the  defects  of  the  Thomas  idler  with  some  added  complications.  The 
same  may  be  said  of  the  Proal  patent  of  1911,  in  which  it  was  proposed  to 
use  separate  pulleys  joined  together  by  axial  helical  springs  and  carried  in 
end-thrust  bearings  similar  to  the  above. 

The  old  difficulties  with  the  cracking  of  belts  were  lessened,  or  avoided 
not  so  much  by  radical  changes  in  belt  construction,  or  by  novelties  in  idler 
construction  as  by  reducing  the  angle  to  which  the  belt  is  bent  along  the  line 
of  flexure  in  troughing.  This  led  to  the  use  of  three-pulley  idlers  with  the  two 
bends  30°,  20°  and  as  low  as  10°  and  to  the  use  of  five-pulley  idlers  where  each 
of  the  four  bends  is  15°.  The  tendency  of  the  present  day  is  in  the  same 
direction,  toward  wide  belts,  shallow  troughing  and  simplicity  in  idler  con- 
struction. 

Efforts  to  Resist  Cutting  and  Abrasion. — Early  experiments  by  Robins 
showed  that  rubber  specially  compounded  resisted  the  action  of  a  sand  blast 
much  better  than  did  other  materials,  the  wear  being  in  the  following  ratios : 
Rubber,  1.0;  rolled  steel,  1.5;  cast  iron,  3.5;  various  cotton  belts,  5  to  9. 
These  ratios  have  been  quoted  by  some  as  showing  the  comparative  worth 
of  these  materials  for  conveying  gritty  substances,  but  the  comparisons  are 
not  valid  when,  as  in  most  belt  conveyors,  the  action  is  not  simple  abrasion, 
but  a  combination  of  cutting  and  abrasion.  It  is  well  known  that  when  a 
belt  with  a  rubber  cover  is  subjected  to  severe  impact  of  large  sharp  pieces, 
the  cover  may  be  cut  through  to  the  fabric,  and  dirt  and  water  may  get  under 
the  cover  and  into  the  fabric,  whereupon  the  belt  fails  by  its  cover  coming 
loose  or  the  plies  separating  while  the  cover  may  still  retain  its  original 
thickness.  The  threads  of  cotton  in  a  rubber  belt  are  to  a  certain  extent 


METAL  REINFORCEMENTS  19 

waterproofed  by  the  layer  of-  "  friction  "  which  covers  each  ply  of  duck, 
but  the  fibers  of  the  threads  are  not  impregnated  with  rubber  and  they  still 
retain  capacity  for  absorbing  moisture..  When  a  cut  penetrates  to  the  duck, 
capillary  absorption  will  spread  any  water  which  enters  there,  and  when  the 
cotton  decays  from  mildew  the  plies  separate  or  the  cover  comes  loose  in  a 
blister. 

Metal  Reinforcements. — The  steeply  inclined  belt  conveyors  known  as 
"  tailings  stackers,"  used  on  gold  dredges  to  carry  off  the  waste,  are  subject 
to  very  severe  cutting  and  abrasion  and  the  action  of  water.  The  material 
runs  fom  fine  gravel  to  rocks  weighing  200  or  300  pounds  and  may  include 
tree  stumps,  pieces  of  lumber  and  anything  else  picked  up  by  the  dredge 
buckets.  Costly  belts  used  in  this  service  have  lasted  only  a  few  weeks  or 
months,  and  since  they  were  often  scrapped  because  of  wear  in  the  middle 
while  the  edges  were  still  good,  efforts  have  been  made  to  add  life  to  these 
belts  by  the  use  of  metal  cleats  riveted  to  the  working  face  (St.  Clair,  1890; 
Manning,  1908;  Cory  &  Dandridge,  1909),  metal  staples  (Folsom,  1906); 
flexible  woven  wire  face  (Hohl .&  Schorr,  1906);  imbedded  wire  coils  (Pattee, 
1916;  Heaton,  1909);  leather  face  (Cook,  1906).  None  of  these  has  come  into 
practical  use;  there  are  objections  to  all  of  them.  Wherever  a  hole  is  made 
through  the  fabric  for  a  metal  reinforcement,  water  and  sand  will  enter; 
if  the  reinforcing  pieces  are  arranged  in  parallel  rows,  the  belt  may  crack  by 
concentration  of  the  bending  along  those  lines  as  it  runs  over  the  troughing 
idlers.  Wire  reinforcement  rusts  out  as  well  as  wears  out;  the  bond  between 
the  metal  and  the  rubber  or  the  fabric  is  generally  imperfect  and  as  the  parts 
separate  under  the  stresses  of  troughing  and  bending  over  pulleys,  water  and 
grit  work  their  way  into  the  belt. 

Other  Protective  Devices. — Another  protective  device  is  shown  in  the 
Vaughan  patent  of  1905,  where  the  main  conveyor  belt  is  partly  covered  by  a 
separate  narrower  belt  that  acts  as  a  protector  to  the  middle  of  the  wider 
belt.  In  the  Voorhees  patent  of  1906,  a  belt  has  a  rubber  cover  in  which 
are  imbedded  cotton  fibers  set  to  expose  their  ends  to  the  impact  and 
abrasion  of  the  material  carried.  Plummer,  in  1906,  made  a  compound  belt 
with  a  solid  woven  cotton  back  for  flexibility,  with  a  wear-resisting  face  of 
stiff  canvas  stitched  on.  In  1916  Bowers  patented  a  rubber  belt  in  which 
the  wearing  face  contained  several  edgewise  layers  of  frictioned  fabric  set 
on  the  bias  so  as  to  take  the  wear  partly  on  the  ends  of  the  cotton  fibers. 

Rubber  Covers. — In  the  rubber-belt  business  as  in  the  rubber-tire  busi- 
ness, it  has  been  found  that  nothing  protects  the  fabric  carcass  of  the  belt  or 
the  tire  so  well  as  a  rubber  cover  or  tread.  Metal  reinforcements  and  other 
protective  devices  add  expense  and  generally  fail  to  protect  the  body  of 
fabric  from  abrasion,  cutting,  and  the  entrance  of  water.  Rubber  covers  are 
depended  upon  to  do  that  in  present-day  practice,  and  in  the  quality  of  the 
covers  and  their  ability  to  withstand  abuse  there  has  been  a  steady  improve- 
ment in  recent  years. 


CHAPTER  III 
BELTS   AND   BELT   MANUFACTURE 

RUBBER  BELTS 

The  Duck. — The  strength  of  the  belt  lies  in  the  duck,  a  cotton  fabric 
which  for  conveyor  and  elevator  belts  differs  from  ordinary  sail  duck  or  canvas 
in  the  fact  that  the  strength  of  the  warp  (lengthwise)  threads  is  considerably 
greater  than  that  of  the  weft  or  filler  (crosswise)  threads.  Duck  for  rubber 
belt  is  graded  as  20-ounce,  28-ounce,  36-ounce,  etc.,  according  to  the  weight 
of  a  piece  36  inches  long  in  the  warp  by  42  inches  wide;  the  warp  threads  are 
usually  larger  and  closer  together  than  the  filler  threads,  and  the  size  of  the 
thread  is  determined  by  the  number  of  spun  yarns  it  is  made  of.  Thus,  one 
weave  of  28-ounce  belt  duck  may  have  a  warp  6  yarns  to  the  thread,  26 
threads  per  inch  and  a  filler  5  yarns  per  thread,  17  threads  per  inch.  Another 
belt  maker  may  use  a  28-ounce  duck  with  a  warp  6X24  and  a  filler  5x14, 
but  with  a  tighter  twist  in  the  threads  to  make  up  the  weight.  The  strength 
of  the  duck  depends  not  only  on  its  weight,  but  on  the  degree  of  twist  in  the 
threads,  and  the  cementing  action  of  the  rubber  depends  upon  the  openness 
of  the  weave  as  well  as  on  the  quality  of  the  rubber.  All  of  these  factors  are 
important;  in  the  best  use  of  them  the  belt  maker  shows  his  knowledge  and  skill. 

Friction. — The  cementing  layer  of  "  friction  "  as  it  is  called  in  the  trade,  is 
a  plastic  mass  of  rubber  to  which  is  added  some  sulphur  for  vulcanization  plus 
certain  compounding  ingredients  which  give  it  that  degree  of  resilience  and 
elasticity  combined  with  resistance  to  distortion  under  load  which  fit  the 
finished  product  for  its  particular  use  and  at  the  same  time  to  the  price  at 
which  the  belt  is  to  be  sold. 

Manufacture. — The  duck  is  first  passed  over  heated  cylinders  to  remove 
most  of  its  moisture;  then  it  is  run  between  the  lower  and  middle  rolls  of  .a 
calender  press  whose  three  rolls  are  heated  by  steam.  The  plastic  mass  of  rub- 
ber is  fed  between  the  top  and  the  middle  roll ;  the  temperature  of  the  two 
rolls  is  so  controlled  that  the  compound  sticks  to  the  middle  roll  and  since  this 
revolves  faster  than  the  lower  roll,  the  rubber  is  pressed  and  wiped  into  the 
fabric  as  the  duck  passes  between  the  two.  When  both  sides  of  the  duck  have 
been  treated,  the  frictioned  fabric  is  cut  into  strips  of  the  desired  width  and  then 
assembled  into  belt.  Thus  the  making  of  an  18-inch  6-ply  belt  starts  with 
an  inner  strip  36|  inches  wide  folded  and  rolled  to  make  2  plies  or  layers  with 
a  butt-joint.  Then  a  strip  about  36f  inches  wide  is  folded  around  with  the 
joint  about  2  inches  from  one  edge,  then  rolled,  making  2  more  plies;  the  outer 
plies  are  made  of  a  strip  37  inches  wide  wrapped  around  the  other  four  with 
its  joint  (which  is  open  about  r£  inch)  located  2  inches  from  the  other  edge 

20 


RUBBER  BELTS  21 

of  the  belt.  If  the  belt  is  not  to  receive  a  rubber  cover,  the  outer  joint  is 
closed  by  a  seam  strip  of  soft  rubber,  see  Fig.  40,  then  the  belt  is  given 
another  pass  through  a  roller  press  which  squeezes  all  the  plies  together  and 
rolls  the  seam  strip  into  and  over  the  outer  joint  in  the  duck.  Rubber  covers 
less  than  yg-  inch  thick  are  generally  calendered  on  to  the  outside  ply;  thicker 
covers  are  rolled  out  in  sheet  form  cut  to  width  and  then  laid  over  the 
assembled  plies. 

In  this  condition  the  belt  is  soft  and  "uncured."  To  vulcanize  or  cure 
it,  the  belt  is  run  between  the  upper  and  lower  platens  of  a  steam-heated 
press,  and  squeezed  at  the  temperature  corresponding  to  40  pounds  steam 
pressure  (280°  to  288°  Fahrenheit)  for  15  or  20  minutes.  In  the  process, 
a  chemical  change  occurs  which  makes  the  rubber  less  sensitive  to  changes 
in  temperature,  increases  its  strength  and  resistance  to  abrasion,  makes  it 
more  durable  on  exposure  to  the  weather  and  more  resistant  to  chemical 
reagents.  If  the  temperature  of  vulcanization  exceeds  300°,  the  cotton  is  apt 
to  be  injuriously  affected  and  the  strength  of  the  belt  will  be  reduced. 

Most  rubber  belts  are  put  under  stretch  in  the  vulcanizing  press  before  the 
platens  close,  and  are  cured  under  stretch,  as  much  as  8  per  cent  of  the  original 
built-up  length  being  removed  in  this  way;  in  some  cases  the  duck  may  be 
stretched  before  it  is  assembled  into  belt. 

Technique  of  Rubber  Manufacture. — This  is  a  complicated  subject;  the 
chemistry  of  the  business  is  not  well  understood,  although  the  effects  of  the 
various  compounding  ingredients  are  well  known.  There  are  at  least  50 
kinds  of  raw  rubber  in  commercial  use,  and  several  dozen  compounding  ingre- 
dients for  belts  alone.  Manufacturers  also  use  several  kinds  of  rubber  substi- 
tutes made  by  oxidizing  vegetable  oils,  like  linseed  oil  and  cottonseed  oil,  and 
there  are  many  grades  of  reclaimed  rubber  used  in  the  business,  some  of 
which  cost  more  than  certain  grades  of  raw  rubber.  The  knowledge  of  proper 
compounding  and  proper  vulcanization  to  fit  belts  for  the  many  uses  to  which 
they  are  put,  comes  from  long  experience,  and  is  one  of  the  most  valued 
assets  of  the  belt  manufacturer.  Technical  works  on  rubber  manufacture 
give  formulas  for  friction  compounds  and  cover  compounds,  but  they  are  of  no 
particular  use  to  users  of  belts.  Each  belt  factory  has  its  own  formulas  and 
they  are  not  made  public. 

The  various  substances  used  in  compounding  rubber  are  not  introduced 
merely  to  cheapen  the  article.  Some,  like  whiting,  are  inert  fillers,  but  there 
are  others,  zinc  oxide  for  instance,  which  within  certain  limits  toughen  the 
rubber,  and  increase  its  tensile  strength  and  its  resistance  to  abrasion.  Some 
ingredients  are  added  to  shorten  the  time  of  vulcanization,  others  to  soften  the 
rubber  to  make  it  more  plastic;  some  of  these  substances  cost  more  than  the  raw 
rubber  itself.  Compounding  is  a  necessity  because  raw  rubber  does  not  possess 
in  itself  all  the  qualities  needed  for  the  friction  nor  the  cover  of  conveyor  and 
elevator  belts.  Whether  the  rubber  used  is  a  cheap  African  rubber  costing  a 
few  cents  a  pound,  or  a  high-grade  Para  or  plantation  rubber  that  cost  in  war 
time  over  a  dollar  a  pound,  it  must  be  compounded  to  bring  out  certain  quali- 
ties which  are  needed  for  the  use  to  which  it  is  put. 


22 


BELTS  AND  BELT  MANUFACTURE 


As  a  result  of  the  attention  which  American  manufacturers  of  rubber 
belts  have  given  to  the  compounding  of  rubber,  there  has  been  within  the 
past  ten  years  a  reduction  in  the  cost  of  the  compounded  rubber  and  at  the 
same  time  an  improvement  in  the  life  and  durability  of  belts,  especially  in 
the  wearing  covers. 

Another  point  aimed  at  in  compounding  is  to  increase  the  life  of  the 
rubber.  In  its  original  state,  when  drawn  from  the  tree,  rubber  is  subject 
to  fermentation  and  putrefaction  like  other  vegetable  juices.  These  proc- 
esses are  arrested  by  smoking  the  liquid  as  is  done  in  the  Brazilian  forests 
or  by  coagulating  it  with  chemicals  as  is  done  with  plantation  rubber  in  the 
East  Indies;  nevertheless  the  raw  rubber  of  commerce  is  to  some  extent 
subject  to  decay  by  the  absorption  of  oxygen  from  the  air.  Rubber  bands, 
which  are  pure  rubber  with  no  addition  except  enough  sulphur  for  vulcaniza- 
tion, show  decided  deterioration  after  a  year  or  two,  but  the  same  rubber 
properly  compounded  to  resist  aging,  would  show  proportionately  less 
deterioration,  although  its  original  elasticity  would  be  much  less  than  that 
of  the  pure  rubber. 

For  the  effect  of  light,  heat  and  age  on  rubber,  see  page  44. 

Various  Rubber  Belts. — The  duck  in  elevator  belts  is  generally  32-ounce. 

Conveyor    belts    are    generally    made    of    28-,    30-,    or    32-ounce    duck; 

special  belts  for  hard  work  may  be  built  of  36-  or  42-ounce  duck.     For 

carrying   light    substances    which    cause    no  wear    on  the  belt    surface  a 

"  friction-surface  "  belt  (Fig. 

m -:V —.•- ;-  "-<     40)    may   be    used,    but    in 

general  service,  including 
grain  conveying,  it  is  cus- 
tomary to  use  a  belt  with  a 
rubber  cover.  Such  a  cover 
in  its  lightest  and  cheapest 
form  (Fig.  41),  is  a  sheath 
of  compounded  rubber  about 
^o  or  j=2  inch  thick  all  around 
the  belt;  it  resists  abrasion 
to  some  degree,  keeps  out 
moisture  and  helps  to  pro- 
long the  life  of  the  friction 
rubber.  When  the  material 
is  heavy  and  the  abrasion 

and  cutting  severe,  the  ^-inch  cover  is  not  enough;  a  heavier  cover  (Fig.  42) 
is  needed  to  make  a  belt  of  balanced  construction,  that  is,  one  that  will  get 
the  benefit  of  the  cover  until  the  friction  rubber  dries  out  and  the  plies  tend 
to  separate.  On  the  other  hand,  it  is  wasteful  to  use  a  cover  too  thick  for 
the  service;  if  the  belt  in  its  carcass  of  fabric  should  wear  out  much  sooner 
than  its  cover,  discarding  the  belt  would  throw  good  rubber  into  the  scrap. 
Straight-ply  Belts. — Most  rubber  conveyor  belts  and  all  transmission 
and  elevator  belts  are  straight-ply  belts,  that  is,  of  uniform  thickness  in  the 


FIG.  40. — 6-ply  Grain  Elevator  Belt  with  Friction 
Surface,  Showing  Seam  Strip. 


RUBBER  BELTS  23 

body  of  fabric.  The  plies  are  held  together  by  the  adhesion  between  the 
duck  and  the  layers  of  friction  rubber;  the  better  the  rubber  compound,  the 
stronger  the  adhesion  and  the  longer11  it  will  retain  its  hold  on  the  duck. 
When  the  rubber  gets  old,  it  loses  its.tenacity,  it  tears  or  separates  easily 
from  the  duck,  and  then  the  plies  come  apart.  The  strength  of  this  adhesion 
is  one  way  to  judge  the  quality  of  a  belt.  The  friction  test  is  shown  in 
Fig.  49. 

Stitched  Belts. — When  belts  are  exposed  to  heat,  the  friction  compound 
tends  to  dry  out  more  quickly  and  lose  its  hold  on  the  fabric.  To  prevent 
the  plies  from  separating  from  this  cause,  they  are  sometimes  stitched 
through  and  through  with  cotton  twine  before  the  cover  is  put  on  and  before 
vulcanizing.  There  are  some  drawbacks  to  this,  and  the  practice  is  not 
general  because  the  twine  must  be  waxed  for  use  in  the  sewing  machine, 
and  the  cover  is  more  apt  to  loosen  from  it  than  from  the  duck. 


FIG.  41. 


FIG.  42. 


FIG.  41. — 8-ply  Elevator  Belt,  with  ^-inch  Rubber  Cover  on  Both  Sides. 

FIG.  42. — 8-ply  Elevator  Belt  with  |-inch  Top  Cover  and  ^-inch  Cover  on  Pulley  Side. 

When  the  wear  from  side-guide  idlers  is  severe  and  the  plies  are  apt  to 
separate  along  the  edges  while  the  body  of  the  belt  is  still  good,  rubber  belts 
are  sometimes  improved  by  a  line  of  stitching  f  inch  from  each  edge  with  a 
second  row  1  inch  from  the  first. 

Belts  to  Resist  Heat. — Ordinary  rubber  belts  do  not  hold  together  well 
when  they  carry  material  at  150°  F.  or  over,  especially  if  the  material  is 
fine  and  holds  its  heat.  If  the  pieces  carried  are  large,  or  if  the  load  is  a 
mixture  of  lumps  and  fines,  the  action  on  the  belt  is  not  so  bad,  because  the 
heat  is  dissipated  more  rapidly  by  the  travel  of  the  belt.  Rubber  belts  are 
made  especially  for  service  in  hot  places  or  for  carrying  hot  materials;  the 
rubber  is  not  vulcanized  to  the  same  degree  as  in  ordinary  belts  and  some- 
times a  layer  of  slow-vulcanizing  rubber  ^  or  YS  m°h  thick  is  inserted 
between  several  of  the  plies  in  the  assembly.  In  the  finished  belt  this  layer 
retains  its  softness  and  tenacity  to  a  good  degree  when  exposed  to  heat  and 
prevents  the  plies  from  coming  apart  too  soon. 


24  BELTS  AND  BELT  MANUFACTURE 

Lamina  Belts. — The  assembly  called  by  this  name  in  the  trade  consists 
in  a  6-ply  belt,  for  example,  of  four  layers  or  plies  of  duck  of  the  full  width 
of  the  belt,  held  together  at  the  edges  by  narrow  strips  ihat  form  a  binding 
like  a  book  cover,  with  an  outside  wrapper  of  duck  which  goes  over  all  to 
form  the  two  outside  plies.  Such  a  belt  has  no  longitudinal  seams  in  its 

body  and  its  edge  is  two  plies  thicker 
than  its  body  (Fig.  43).  This  makes 
a  stiff  edge  to  resist  pressure  against 
side-guide  idlers,  and,  at  the  same 
time,  the  rubber  cover  is  thicker 
over  the  surface  of  the  belt  than 
near  the  edges. 

Stepped-ply    Belts. — This    style 
FIG.  43.—"  LgninaJ  Construction  of  a       of  belt  (Fig    32)  has   already  been 

mentioned.  As  now  furnished  by 

Robins,  the  belt  is  built  up  in  two  ways:  1.  Rubber  cover  f  inch  thick  in 
center  with  1  ply  of  fabric  less  there  than  at  the  edges;  2.  Rubber  cover 
•fg  inch  thick  in  center  with  2  plies  less  there  than  at  the  edges.  The  cover 
on  the  carrying  surface  is  about  TQ  inch  thick  near  the  edges  in  each  case. 

Stepped-ply  belts  are  made  by  several  manufacturers  with  various  assemblies 
of  plies  and  covers. 

Edges  of  Rubber  Belts. — Wear  on  the  edges  of  conveyor  belts  is  a 
common  cause  of  their  failure.  It  may  come  from  the  use  of  side-guide 
idlers  to  correct  bad  alignment  of  the  conveyor  or  to  counteract  faults  in 
the  design  of  the  troughing  idlers.  The  belt  may  rub  against  the  delivery 
chute  at  the  end  pulley,  or  in  the  tripper,  or  it  may  interfere  with  idler 
brackets  on  the  return  run  or  with  the  supporting  framework  of  the  con- 
veyor. In  rubber  belts  destruction  of  the  edge  exposes  the  cotton  duck  to  the 
action  of  moisture  and  dirt;  the  fibers  mildew,  the  friction  rubber  gives  way 
and  the  plies  separate. 

There  are  several  ways  of  making  the  edge  of  a  rubber  belt.  The  Metzler 
edge  (patented  1910),  used  by  two  manufacturers,  protects  the  outer  ply  by 
a  thickness  of  rubber  continuous  with  the  top  cover  (Fig.  44)  and  has  an  inser- 
tion of  rubber  under  the  outer  ply  to  protect  the  assembled  inner  plies,  so  that 
the  latter  may  have  some  protection  if  edge  wear  should  progress  beyond  the 
outer  ply  of  the  belt.  Another  method  of  construction  is  to  bring  the  top 
cover  around  the  edge  and  join  it  to  the  rubber  cover  on  the  pulley  side  of  the 
belt  (Figs.  42  and  45).  On  tailings  stackers  (see  page  19)  the  conveyor  align- 
ment is  apt  to  be  bad  and  the  belt  may  have  to  be  held  in  place  by  side-guide 
idlers.  The  wear  on  the  edge  of  the  belt  combined  with  the  wet  and  grit  may 
make  it  advisable  to  protect  the  edge  by  an  extra  thickness  of  rubber  there 
(Fig.  46).  The  5-ply  belt  shown  in  Fig.  47  has  a  very  thick  edge  to  resist  side 
wear  and  a  rubber  cover  |  inch  thick,  both  of  which  are  held  to  the  body  of 
fabric  by  a  layer  of  "  tie-gum,"  or  cement,  in  which  is  imbedded  1  ply  of  light- 
weight coarse-mesh  fabric  known  as  "  cider-press  cloth."  In  making  this 
belt  the  assembled  plies  are  covered  with  a  layer  of  strong  adhesive  rubber, 


RUBBER  BELTS 


25 


better  than  that  used  in  the  friction;  the  open-mesh  cloth  is  laid  on  top  and 
brought  around  under  each  edge  for  a  few  inches;  then  the  cover  is  laid  on. 
When  the  belt  is  put  under  pressure  and  vulcanized,  the  layer  of  tie-gum,  or 
cementing  rubber,  with  the  imbedded  fabric  comes  into  close  and  thorough 
contact  with  the  rubber  of  the  cover  askd  the  friction  of  the  duck  and  holds 
the  two  together  with  a  bond  stronger  than  that  which  ordinarily  exists  between 
the  cover  and  the  body  of  the  belt.  Along  the  edge  the  imbedded  fabric  gives 


FIG.  44.— (Goodyear  Tire 
and  Rubber  Co.) 


FIG.  45.— (B.  F.   Goodrich 
Rubber  Co.) 


&m  H 


FIG.  46. — (B.   F.   Goodrich 
Rubber  Co.) 


FIG.  47. — (B.   F.   Goodrich 
Rubber  Co.) 


FIG.  44. — 5-ply  Conveyor  Belt  with  £-inch  Top  Cover  and  Metzler  Edge. 

FIG.  45. — 6-ply  Conveyor  Belt  with  f-inch  Top  Cover  and  Rounded  Edge. 

FIG.  46. — 6-ply  Dredge  Belt  with  ^-inch    Top  Cover  and  ^-inch  Rubber  on  Edge. 

Cover  on  Pulley  Side  r^-inch. 
FIG.  47. — 5-ply  Conveyor  Belt  Extra  Heavy  Duck,  with  f-inch  Top   Cover  and  i-inch 

Edge  Cemented  to  Fabric  by  a  Layer  of  Open-mesh  Cloth  Imbedded  in  "  Tie-gum." 

Cover  on  Pulley  Side  r^-inch. 


some  protection  to  the  body  of  the  belt,  but  its  greater  use  is  to  form  a  strong 
bond  between  the  outer  ply  and  the  rubber  along  the  edge,  and  to  prevent 
the  latter  from  being  pulled  off  in  a  strip  should  the  belt  encounter  an  obstacle 
in  its  travel  or  meet  with  an  accident  in  handling  or  erection.  (See  also 
"  Reinforced  Covers,"  page  29.) 

Rubber  Covers. — The  purpose  of  a  wearing  cover  on  a  rubber  belt  is  to 
protect  the  body  of  fabric,  to  an  economical  degree,  from  abrasion  and  cutting, 
and  from  the  entrance  of  moisture.  In  giving  this  protection  "  to  an 


26  BELTS  AND  BELT  MANUFACTURE 

economical  degree,"  the  cover  must  not  be  too  thin  nor  too  thick.  If  too 
thin,  the  plies  may  be  cut  so  badly  that  the  belt  is  thrown  away  while  the 
friction  is  still  good  and  before  the  plies  have  begun  to  separate;  if  too 
thick,  the  belt  may  reach  the  scrap  pile  while  there  is  still  good  rubber  in 
the  cover. 

If  the  belt  has  a  good  friction  and  enough  plies  to  transmit  the  pull 
easily  and  safely,  and  if  the  operating  conditions  are  good,  it  pays  to  use  a 
cover  that  will  develop  the  full  life  of  the  friction  rubber ;  but  if  the  operating 
conditions  are  bad,  if  the  belt  is  likely  to  be  ruined  by  neglect  or  accident, 
if  it  is  too  light  for  the  tensile  stress,  or  if  the  quality  of  the  friction  is  not 
good,  then  it  is  wasting  money  to  put  a  good  cover  on  the  belt.  The  proper 
balance  between  the  quality  and  thickness  of  the  body  of  fabric  and  the 
quality  and  thickness  of  the  rubber  cover  differs  according  to  the  material 
handled,  the  care  in  loading  and  discharging,  the  hours  of  service,  the  length 
of  the  conveyor,  the  importance  of  the  installation  and  the  degree  of  over- 
sight and  maintenance.  These  conditions  are  never  exactly  the  same  in 
any  two  conveyors,  and  hence  there  is  no  general  rule  for  the  thickness  of 
rubber  covers. 

Thickness  of  Rubber  Covers. — In  average  practice,  the  aim  is  to  make 
the  cover  so  thick  that  the  cut  made  by  the  impact  or  drag  of  a  sharp-cornered 
piece  at  the  loading  point  of  the  conveyor  will  not  penetrate  through  the  cover 
into  the  fabric  of  the  belt.  A  cut  might  injure  the  tensile  strength  of  the  belt, 
but  the  greater  danger  is  that  water  or  dirt  may  get  through  into  the  cotton 
and  cause  separation  of  the  plies  or  blistering  of  the  cover.  When  the  cover 
starts  to  blister,  the  trouble  is  apt  to  be  made  worse  by  the  kneading  action 
of  the  idler  pulleys.  A  blistered  cover  may  catch  at  a  chute  or  in  a  tripper  and 
do  serious  damage. 

For  run-of-mine  coal  and  heavy  ore,  covers  are  generally  Y&  incn  thick. 

For  crushed  coal  and  ores,  covers  are  generally  |  inch  thick. 

For  fine  materials  not  extremely  abrasive,  covers  are  generally  YG  inch 
thick. 

Resistance  of  Rubber  Covers  to  Combination  of  Impact  and  Abrasion. — 
The  protection  which  a  good  rubber  cover  gives  to  a  belt  can  be  seen  in 
Fig.  48,  which  shows  the  appearance  of  six  samples  of  belting  after  a  test 
of  one  hundred  hours  made  by  the  author.  Two  pieces  of  6-ply  stitched  canvas 
belt,  two  pieces  of  6-ply  high-grade  rubber  belt  with  |-inch  cover  and  two  pieces 
of  medium-grade  belt  6-ply  with  f-inch  cover  were  tumbled  together  for  one 
hundred  hours  in  a  cleaning  mill  with  charges  of  hard  iron  castings  weighing 
about  750  pounds  per  charge.  Weights  were  taken  at  the  time  new 
charges  of  sandy  castings  were  put  into  the  cleaning  mill. 

The  pieces  were  all  6  inches  square  at  the  start  and  were  cut  so  that  one 
edge  in  each  specimen  was  the  edge  of  a  conveyor  belt.  The  high-grade 
belt  distinguished  by  the  hole  drilled  in  the  test  specimens  showed  least 
loss  of  size  and  weight,  and  the  canvas  belt  lost  most.  The  pulley  side  of 
the  rubber  belts  showed  more  wear  than  the  other  side,  but  the  friction  rubber 
offered  considerable  resistance  to  the  combined  action  of  the  sandy  grit 


RUBBER  BELTS 


27 


and  the  blows  which  it  received  in  the  cleaning  mill.     Table  1  gives  the 
record  of  weights  and  losses  during  the  one  hundred  hours. 

Quality  of  Rubber  Covers. — There  is  a  direct  relation  between  the  tensile 
strength  of  rubber  and  its  resistance  to  abrasion;  hence  it  is  possible  to 
secure  resisting  quality  in  a  rubber  ,$over  by  requiring  it  to  show  a  certain 
tensile  strength.  The  strength  of  compounded  rubber  for  covers  may  vary 
in  different  belts  from  a  few  hundred  pounds  to  over  2000  pounds  per  square 
inch;  if  specifications  are  written  to  require  a  certain  tensile  strength,  the 
test  pieces  and  the  manner  of  testing  should  be  according  to  methods  which 
are  agreed  upon  as  correct,  such  as  those  described  in  Bulletin  38  of  the 


FIG.  48. — Samples  of  Belt  after  100  Hours  of  Impact  and  Abrasion. 

Bureau  of  Standards,  Washington,  D.  C.  Unless  the  tests  are  conducted 
in  such  a  manner,  the  results  may  be  open  to  controversy. 

Table  2  (Bureau  of  Standards)  gives  the  results  of  tests  of  four 
specimens  of  compounded  rubber. 

Some  specifications  for  belts  carrying  run-of-mine  coal  have  required  the 
cover  to  show  650  pounds  per  square,  inch  breaking  strength,  and  a  strip 
of  it  1  inch  wide  with  marks  2  inches  apart  is  required  to  stretch  to  6^  inches 
between  marks  without  breaking  and  without  showing  more  than  YQ  inch 
permanent  stretch  when  measured  immediately  after  the  test.  Another 
specification  for  a  belt  with  ^-inch  cover,  handling  heavy  ore  required  a 
piece  to  stretch  from  2  inches  between  marks  to  11  inches  before  breaking. 
The  thin  covers  TO  or  -^  inch  thick,  used  on  grain  belts,  should  be  able  to 
pass  the  following  test.  "  The  outer  ply  shall  be  stripped  from  a  piece  of  belt 


28 


BELTS  AND  BELT  MANUFACTURE 


TABLE  1.— COMPARATIVE  RESISTANCE  OF  BELTS  TO  BLOWS 
AND  ABRASION 

(Specimens  6  inches  square.     See  Fig.  48) 


Stitched  Canvas 

Medium-Grade 

High-Grade 

Belt 

Rubber  Belt 

Rubber  Belt 

Hours  of  Test 

Specimen  1, 

Specimen  2, 

Specimen  1, 

Specimen  2, 

Specimen  1, 

Specimen  2, 

Weight 

Weight 

Weight 

Weight 

Weight 

Weight 

Grams 

Grams 

Grams- 

Grams 

Grams 

Grams 

At  start 

203.5 

204 

305 

304.7 

305.8 

314 

7 

201 

202 

301 

300 

301 

310 

14 

192 

191 

295 

295 

296 

306 

21 

185 

186 

289 

290 

292 

301 

28 

170 

171 

280 

281 

285 

295 

35 

155 

155 

269 

272 

279 

286 

42 

140 

140 

263 

266 

271 

281 

49 

133 

131 

257 

258 

263 

270 

56 

127 

124 

254 

255 

257 

267 

63 

115 

115 

247 

247 

251 

259 

71 

108 

107 

244 

245 

248 

257 

79 

102 

101 

240 

240 

245 

254 

87 

93 

93 

235 

236 

241 

247 

100 

90 

89 

234 

235 

240 

246 

Total    loss    in 

grams  .         .  . 

113.5 

115 

71 

69.3 

65.8 

68 

Average  loss  in 

* 

per  cent  

56.0 

23.0 

21.5 

TABLE  2.— TESTS  OF  COMPOUNDED  RUBBER 
(Bureau  of  Standards) 


Specimen  Number 

1 

2 

3 

4 

Pulling  speed,  inches  per 
minute  

5 
2495 
605 

25 
2690 
635 

45 
2720 
635 

5 

1900 
465 

25 
1940 
500 

45 
1970 
490 

5 
375 
340 

25 
430 
360 

45 
465 
375 

5 
340 
105 

25 
390 
115 

45 
430 
120 

Breaking  strength,  pounds 
per  square  inch 

Ultimate  elongation,  per 
cent 

and  bent  over  flat  on  itself  with  the  rubber  cover  outside,  and  a  second  bend 
made  at  right  angles  to  the  first  bend.  No  cracks  shall  appear  anywhere  on 
the  surface  when  the  bent  and  folded  ply  is  pressed  as  hard  as  possible 
between  the  thumb  and  finger."  The  following  is  from  a  specification  for 
belts  with  -^-inch  covers  for  elevating  and  conveying  sugar  and  char  in  a 
sugar  refinery.  "A  piece  of  the  cover  £  inch  wide  shall  stretch  without 
breaking  from  2  inches  between  marks  to  3  inches  between  marks;  upon 


RUBBER  BELTS  29 

immediate  release,  the  piece  will  rest  five  minutes  and  must  then  not  show 
more  than  |-inch  elongation  in  the  2  inches." 

From  an  inspection  of  Figs.  52  and  53,  page  45,  it  is  apparent  that  the  age 
of  the  rubber  specimen  has  a  great  effect  upon  its  tensile  strength  and  elongation. 
All  rubber  compounds  do  not  deteriorate  alike,  as  may  be  seen  by  comparing 
G7  with  (r4.  G4,  when  fresh,  showed  higher  than  G7  both  in  tensile  strength 
and  elongation,  but  was  lower  in  both  respects  after  six  months.  This  point 
is  not  covered  by  any  specifications  in  commercial  use.  So  far  as  belt  manu- 
facturers are  concerned,  one  maker  may  rate  a  certain  grade  of  cover  so  far 
under  its  maximum  strength  that  it  would  pass  the  tensile  test  at  any  time 
during  the  normal  or  expected  life  of  the  belt.  Another  maker  might  rate  the 
same  cover  much  higher  with  a  fair  certainty  that  it  would  pass  the  test  in  the 
time  between  placing  the  order  and  acceptance  and  payment. 

It  is  therefore  not  an  easy  matter  to  get  a  good  cover  merely  by  writing 
a  specification  for  it.  If  reliance  is  placed  wholly  on  the  specification,  the 
requirements  must  be  written  with  skill  and  wisdom,  and  the  tests  made  and 
followed  up  with  exactness  and  persistence.  It  is,  however,  quite  practi- 
cable to  put  the  burden  of  responsibility  on  the  manufacturer;  there  are  a 
number  of  makers  of  rubber  belts  who  have  long  experience  in  the  business 
and  whose  skill  and  knowledge,  supplemented  by  continual  test  and  research, 
place  them  in  a  position  to  know  what  a  good  cover  is,  and  how  to  make  it. 

Reinforced  Covers. — When  the  conditions  of  loading  are  such  that  belts 
naturally  wear  through  the  cover  near  the  middle  while  the  edges  of  the  cover 
are  still  good,  it  may  pay  to  use  a  stepped-ply  belt,  or  a  straight-ply  belt  in 
which  the  cover  is  thickened  toward  the  middle.  The  original  belt  of  this 
latter  style  (see  Fig.  31),  did  not  run  well  on  45°  and  35°  troughing  idlers 
and  was  superseded  by  the  stepped-ply  belt.  In  recent  years  it  has  been 
revived  by  several  manufacturers;  it  can  be  used  to  advantage  where  the 
abrasion  is  severe  in  the  middle  of  the  belt  and  where  the  depth  of  troughing 
compared  with  the  width  of  the  belt  is  not  too  great.  The  extra  thickness 
is  made  by  applying  a  strip  of  rubber  to  the  top  of  the  regular  cover  before 
pressing  and  vulcanizing.  One  maker's  standard  practice  for  such  reinforced 
covers  is  to  make  the  strip  Y$  inch  thick  and  half  as  wide  as  the  belt  in  sizes 
up  to  32  inches.  For  wider  belts,  the  extra  yg-inch  thickness  runs  to  within 
3  inches  of  each  edge. 

Covers  with  Reinforcing  Fabric. — Important  belts  with  very  thick  covers 
may  have  imbedded  in  the  rubber  of  the  cover  a  "  floating  ply  "  of  open- 
mesh  fabric  or  of  duck  to  resist  the  tendency  of  sharp  heavy  lumps  to  gouge 
pieces  out  of  the  cover.  The  following  paragraphs  from  a  specification 
issued  by  a  large  mining  company  refer  to  48-inch  belts  in  long  conveyors 
handling  hard,  heavy  ore  in  pieces  averaging  5  inches,  but  ranging  up  to 
15  inches. 

"  Rubber  Covers. — All  belts  to  have  a  covering  of  high-grade  rubber  on 
the  carrying  side  not  less  than  I  inch  thick.  Throughout  the  center  part  of 
this  cover  on  the  carrying  side  is  to  be  inserted  1  ply  of  duck,  known  as  a 
'  floating  ply,'  the  total  thickness  of  cover  and  ply  to  be  J  inch.  The  cover 


30  BELTS  AND  BELT  MANUFACTURE 

on  the  back  of  the  belt  shall  be  YG  mch  thick.  The  edges  of  the  belt  to  be 
rounded  and  the  rubber  covering  not  less  than  ^  inch  thick.  The  cover  on 
both  sides  to  withstand  the  action  of  the  dry  climate  without  hardening  so 
that  its  elasticity  and  toughness  shall  not  be  impaired." 

"  Cohesion  of  Cover.1 — There  is  to  be  placed  between  the  cover  and  the 
first  ply  of  duck,  1  ply  of  open- woven  fabric  known  as  '  cider-press  cloth,' 
this  cloth  being  carried  around  the  edges  and  imbedded  in  frictioned  rubber, 
the  total  thickness  of  the  top  cover  with  floating  ply  and  cider-press  cloth 
being  |  inch.  The  adhesion  between  the  cover  and  the  cider-press  cloth 
shall  be  such  that  in  case  of  accidental  contact  with  projecting  machinery, 
chutes,  etc.,  the  cover  will  break  before  it  tears  loose  from  the  fabric.  The 
adhesion  between  the  cider-press  cloth  and  the  duck  shall  show  the  same 
friction  strength  as  between  the  plies,  i.e.,  20  pounds." 

Tearing  and  Gouging  of  Rubber  Covers. — A  strip  of  good  cover  stock 
|X£  inch  cannot  be  stretched  to  the  breaking  point  by  the  strength  of  a 
man's  hands;  but  by  a  tearing  action  starting  at  a  nick  in  one  edge  of  the 
strip,  it  can  be  pulled  apart  with  the  fingers.  Covers  are  apt  to  be  torn  in 
this  way  by  sharp  pieces  jamming  under  skirt-boards  that  are  set  wrong,  by 
the  chute  filling  up  at  the  discharge  end  or  in  a  tripper,  stopping  the  con- 
veyor while  loaded  so  that  some  material  dribbles  over  a  pulley  and  catches 
between  the  chute  and  the  belt,  by  steel  chutes  or  tools  falling  down  on  the 
belt,  or  by  carelessness  in  handling  the  belt  in  the  roll  or  in  pulling  it  into 
place  over  the  idlers.  Accidents  like  these  will  tear  any  kind  of  rubber 
cover,  good  or  poor.  If  large  pieces  of  the  cover  rip  loose  from  the  top  ply 
with  a  clean  separation,  the  belt  may  be  defective,  but  it  should  not  be 
condemned  because  the  cover  does  not  resist  gouging  or  tearing. 

There  is  no  direct  ratio  between  the  tensile  strength  of  rubber  and  its 
resistance  to  a  tear  or  shear,  although  in  general,  a  high  tensile  cover  stock 
is  less  likely  to  tear  than  one  of  inferior  strength  in  tension.  There  is  appar- 
ently a  contradiction  where  the  specification  quoted  above  calls  for  20 
pounds  friction  pull  per  inch  (see  also  page  35)  between  cover  and  top  ply 
and  at  the  same  time  says  that  the  cover  must  break  before  it  tears  loose. 
It  is,  however,  a  valid  requirement,  because  while  the  tensile  value  of  a 
strip  of  cover  1  inch  wide  is  much  greater  than  20  pounds,  nevertheless,  in 
any  good  belt,  the  cover  will  tear  before  it  will  pull  loose.  It  is  better  that 
it  should;  a  tear  can  be  cemented  and  patched,  but  a  loose  cover  can  never 
be  fastened  on  again  to  stay. 

Specifications  for  Rubber  Belts. — Rubber  belts  came  into  use  for  han- 
dling grain  about  1870;  for  years  after  that,  they  were  generally  sold  on  the 
representations  of  their  makers  as  to  quality.  The  technique  of  manufac- 
ture was  not  well  developed  in  the  early  years,  but  some  of  the  belts  were  of 
remarkably  good  quality.  The  late  Samuel  W.  Neall,  who  had  charge  of 
the  Washington  Avenue  Grain  Elevator  in  Philadelphia,  for  many  years, 
related  the  following:  When  the  two  galleries  on  the  pier  were  erected  in 

1  Fig.  47  illustrates  the  "tie-gum  "  construction  described  in  this  paragraph.  See 
also  Fig.  239. 


METCALFS  SPECIFICATIONS  FOR  GRAIN  BELTS  31 

1873,  two  36-inch  belts  about  800  feet  long  were  installed.  In  1900  the  two 
galleries  were  torn  down  and  replaced  by  a  single  one  twice  as  long;  a 
new  36-inch  belt  was  put  in  and,  parallel  to  it,  a  1600-foot  belt  made  by 
joining  the  two  old  ones.  The  new  belt  lasted  seven  years,  the  old  belts 
were  still  there  and  in  use  when  the  elevator  was  dismantled  in  1916,  forty- 
three  years  after  they  were  originally  installed.  When  the  Pennsylvania 
Railroad  Company's  Girard  Point  Elevator  was  torn  down  in  1916,  the 
original  36-inch  4-ply  rubber  belts  put  in  in  1882,  34  years  before,  were 
still  in  regular  use.  They  were  700  feet  long,  and  ran  flat  with  portable 
concentrators  at  loading  points  only. 

As  the  business  grew,  the  number  of  belt  manufacturers  increased,  and 
competition  for  business  brought  on  the  market  many  belts  of  poor  quality. 
Some  makers  probably  did  not  know  how  a  good  belt  should  be  built.  In 
the  grain  business,  this  led  to  the  use  of  detailed  specifications  for  rubber 
belts.  A  typical  set  of  specifications  is  that  issued  by  the  John  S.  Metcalf 
Co.  of  Chicago.  The  following  is  the  1913  edition: 

METCALFS  SPECIFICATIONS  FOR  GRAIN  BELTS 

1.  The  belts  shall  be  first  class  in  quality,  of  standard  manufacture,  fully 
up  to  the  grade  specified  and  of  a  light  gray  color.     All  duck  used  in  the 
construction  of  the  belts  shall  be  of  the  best  quality.     In  all  belts  a  piece  of 
duck  36X42  inches  shall  weigh  not  less  than  32  ounces. 

2.  The  tensile  strength  of  a  piece  of  duck  1  inch  wide  shall  not  be  less 
than  350  pounds  in  the  direction  of  the  warp.     This  shall  be  the  average 
strength  of  the  entire  width  of  duck  tested  in  pieces  4  inches  wide  or  wider, 
with  the  jaws  of  the  testing  machine  not  less  than  1  inch  apart. 

3.  The  several  plies  shall  be  thoroughly  cemented  together  with  first- 
class  quality  of  Para  rubber  compound,  making  such  an  adhesion  between 
the  different  plies  of  duck  that  it  will  stand  the  following  test,  viz.: 

4.  The  test  shall  be  made  by  cutting  a  strip  1  inch  wide,  running  longi- 
tudinally of  the  belt.     The  various  plies  shall  be  separated  at  one  end  and 
the  strip  suspended  by  attaching  by  its  upper  end,  and  a  weight  of  10  pounds 
shall  be  attached  to  the  lower  end  of  the  strip  to  keep  it  in  a  vertical  position. 
Then  the  other  plies  shall  be  pulled  off,  one  at  a  time,  by  attaching  a  13- 
pound  weight  to  the  upper  end  of  the  outer  ply.     A  coil  spring  shall  be  placed 
between  the  upper  end  of  the  ply  tested  and  the  weight.     No  test  shall  be 
made  between  the  last  two  plies  on  the  strip. 

5.  Under  the  above  conditions  the  plies  must  not  separate  faster  than 
at  the  rate  of  2  inches  in  one  minute.     The  cementing  compound  when  pulled 
apart  shall  show  there  is  ample  rubber  in  its  composition  to  insure  its  lasting 
quality,  and  it  shall  also  show  a  long,  clinging,  fibrous  adhesion  to  the 
duck. 

6.  All  duck  used  in  the  manufacture  of  the  belts  shall  be  of  the  widths, 
also  the  joints  located  only,  as  shown  on  blue  printed  sheet  attached.     (Fig. 
50.) 


32  BELTS  AND  BELT  MANUFACTURE 

7.  The  outside  covering  shall  be  a  coat  of  rubber  not  less  than  ^  of  an 
inch  thick,  evenly  put  on,  thoroughly  vulcanized  and  finished. 

8.  Shop  splices  across  the  belts  shall  not  come  closer  than  10  feet  to 
the  field  splice  in  any  conveyor  belt. 

9.  The  belts  shall  be  straight,  well  stretched  and  pressed.     A  sample 
of  the  belt  not  less  than  24  inches  long  and  22  inches  wide  must  be  submitted 
to  the  Engineers,  John  S.  Metcalf  Co.,  for  their  approval  before  the  belts 
are  manufactured;    also  a  sample  of  duck  36X42  inches.     These  samples 
shall  receive  the  written  approval  of  the  Engineers  before  the  belts  are  man- 
ufactured.    The  samples  approved  in  writing  by  the  Engineers  will  be  held 
by  them  to  compare  with  the  belts  when  delivered.     If  they  are  not  equal  to 
the  samples  they  will  not  be  accepted. 

10.  The  Engineers  may  cut  into  the  belts  at  any  point  and  make  such 
tests  as  they  may  consider  necessary  in  order  to  determine  whether  the 
quality  of  the  belts  is  uniform  and  up  to  the  grade  specified. 

11.  The  testing  of  the  belts  will  be  done  within  three  months  after  the 
time  the  belts  arrive  on  the  ground  and  belts  must  conform  to  these  specifi- 
cations, and  to  the  samples  submitted  and  approved,  at  any  time  they  are 
tested  within  said  three  months. 

12.  The  belts  furnished  shall  be  equal  to  these  specifications  and  also 
equal  to  the  samples  submitted  and  approved.     If  the  belts  as  furnished 
do  not  come  up  to  the  specifications,  or  samples  submitted  and  approved, 
the  Company  shall  have  the  privilege  of  running  them  until  new  belts  are 
supplied   and   can   be  installed   without  inconveniencing  said   Company; 
and  the  manufacturer  shall  at  his  own  expense,  take  them  out  at  such  time 
as  may  be  ordered  by  the  Company  and  replace  them  with  belts  that  do 
conform  to  these  specifications,  and  are  equal  to  the  samples  submitted  and 
approved. 

13.  The  manufacturer  shall  guarantee  that  the  belts  will  not  blister, 
nor  separate  in  the  plies  or  at  the  seams,  within  one  year  from  the  date  of 
installation;  and  shall  guarantee  to  furnish  and  install  new  belts,  complying 
with  these  specifications,  if  such  defects  occur;    and  shall  take  out  the 
defective  belts  at  his  own  expense.     The  manufacturer  shall  not  be  allowed 
anything  for  the  service  obtained  from  belts  which  are  replaced  by  other 
belts. 

14.  All  of  the  elevator  belts  shall  be  accurately  punched  for  bucket  bolts 
in  rows  across  the  belt;  the  rows  being  at  right  angles  to  the  length  of  the 
belt. 

15.  The  Engineers,  or  the  Company,  shall  supply  the  manufacturer 
with  a  drawing  showing  the  size  and  spacing  of  the  bolt  holes,  or  shall  fur- 
nish a  template  for  this  purpose. 

16.  In  the  above  specifications  Engineers  mean  John  S.  Metcalf  Co.; 
Company  means  the  Company  owning  the  elevator  in  which  the  belts  are 
to  be  installed. 

Comment  on  Metcalf  s  Specifications. — Since  these  specifications  and 
similar  ones  based  on  them  are  frequently  referred  to  in  buying  rubber 


METHOD  OF  TESTING  FABRIC  33 

belts,  the  following  comment  on  the  numbered  paragraphs  may  be  of 
interest. 

If  1.  "  First-class  in  quality  "  should  be  qualified  by  the  words  "  for 
the  purpose  intended."  Belts  for  "coal  and  ore  are  generally  of  higher 
"  class  "  than  grain  belts.  "  LighUgray  color  "  refers  to  the  appearance  of 
the  finished  belt  with  the  "  bloom  "  still  on  it,  not  to  the  color  of  the  rubber 
in  the  belt  as  some  persons  have  thought. 

*f[  2.  It  is  not  a  simple  matter  to  test  the  strength  of  belt  duck.  If  a 
test  is  required,  the  method  of  making  it  should  be  agreed  upon.  In  recent 
years  most  belt  manufacturers  test  their  duck  before  cutting  it  up  for  belts, 
but  their  methods  of  testing  are  not  all  alike  and  their  numerical  results  are 
seldom  comparable.  The  following  statement  is  by  the  Goodyear  Tire  & 
Rubber  Co.,  Akron,  Ohio: 

METHOD  OF  TESTING  FABRIC  AS  EMPLOYED  BY  THE  GOOD- 
YEAR  TIRE   &    RUBBER   CO. 

There  are  a  large  number  of  methods  in  use  for  testing  the  tensile  strength 
of  fabric  and  finished  belts,  the  most  of  which  have  received  some  recognition. 
The  same  piece  of  duck  may  show  a  tensile  strength  of  300  pounds  or  700 
pounds  or  any  intermediate  value,  depending  on  the  method  chosen. 
When  the  same  duck  is  built  into  a  belt  and  the  belt  tested,  an  entirely 
different  tensile  strength  value  may  be  obtained.  This  is  due  to  the  fact 
that  the  same  methods  of  testing  are  not  adapted  to  testing  both  raw  duck 
and  finished  belts,  rather  than  to  any  appreciable  change  in  the  strength  of 
the  duck  itself  during  the  building  operation. 

Therefore,  whenever  referring  to  any  such  tensile  strength  figures,  it  is 
absolutely  imperative  that  the  exact  details  of  the  testing  methods  be 
specified. 

None  of  the  methods  which  have  been  devised  up  to  the  present  time 
definitely  determine  what  we  refer  to  as  the  "  true  strength  "  of  duck, 
although  much  research  has  been  done  on  this  problem.  The  most  prac- 
tical methods  are  known  either  as  "  Strip  "  or  "  Grab  "  methods. 

Strip  tests  are  made  on  specimens  raveled  down  to  a  definite  width, 
usually  1  inch  wide  or  else  to  a  definite  number  of  threads.  All  four  jaws 
of  the  testing  machine  must  be  wider  than  the  sample  in  order  to  thoroughly 
grip  all  the  threads  to  be  tested.  This  method  gives  results  which  are  lower 
than  the  "  true  strength  "  because  the  outside  threads  pull  themselves  free 
from  the  rest  of  the  fabric. 

The  Bureau  of  Standards  advocates  a  Strip  method  and  it  is  probable 
that  it  is  slightly  more  accurate  than  any  of  the  Grab  methods,  but  their 
method  is  not  generally  adopted  because  of  the  great  expense  in  preparing 
the  samples. 

Test  specimens  for  the  Grab  method  are  cut  wider  than  the  jaws  and  are 
not  raveled  to  any  definite  width.  One  of  the  four  jaws  of  the  Test  machine 
is  usually  1  inch  wide,  and  the  other  three  jaws  are  usually  2  inches  wide, 


34  BELTS  AND  BELT  MANUFACTURE 

thus  grabbing  firmly  a  section  of  duck  exactly  1  inch  wide.  The  results  by 
this  method  are  higher  than  the  "  true  strength  "  because  in  reality  more 
than  1  inch  wide  of  fabric  is  under  tension.  However,  the  results  by  this 
method  are  fully  as  comparative  as  by  the  Strip  method. 

Goodyear  tests  every  roll  of  belt  fabric,  and  those  rolls  which  fail  to 
meet  a  definite  standard  are  rejected.  Inasmuch  as  at  least  six  specimens 
are  .necessary  from  each  roll  (three  from  the  warp  and  three  from  the  filler), 
it  is  found  that  the  Strip  method  is  too  expensive  for  the  slight  advantage 
gained  by  this  method  over  the  Grab  method.  It  has,  therefore,  been 
necessary  for  us  to  use  a  Grab  method  and  the  following  details  are  standard 
with  us: 

The  specimens  are  cut  2f  X6  inches  and  placed  in  a  Scott  Fabric  Testing 
Machine,  equipped  with  a  pair  of  2-inch  wide  jaws  on  one  end  and  on  the 
other  end,  a  1-inch  jaw  bearing  against  a  2-inch  jaw.  The  two  pairs  of  jaws 
are  3  inches  apart  at  the  start  of  the  test  and  are  separated  at  the  rate  of 
20  inches  per  minute.  The  machine  indicates  the  maximum  tensile  at  the 
time  the  fabric  breaks.  This  figure  is  then  corrected  for  moisture. 

Cotton  before  being  frictioned  absorbs  moisture  from  the  air  very  readily. 
The  Bureau  of  Standards  has  found  that  the  tensile  strength  of  cotton  fabric 
increases  7  per  cent  with  every  increase  of  1  per  cent  in  the  moisture  con- 
tents. The  strength  decreases  again  with  the  drying  out  of  the  fabric  in 
the  same  proportion;  therefore,  we  determine  the  moisture  content  on  every 
sample  of  duck  and  the  tensile  strength  is  corrected  to  the  standard  basis  of 
6  per  cent  moisture  by  the  above  method. 

H  3.  "  First-class  quality  " — the  13-pound  friction  test  called  for  in  the 
next  paragraph  really  specifies  the  quality.  Friction  that  tests  18  or  20 
pounds  is  of  higher  quality.  "  Para  "  rubber  from  Brazil  was  once  the 
standard  of  quality;  now  over  75  per  cent  of  the  world's  rubber  comes  from 
plantations  in  Ceylon,  India,  and  Sumatra,  and  as  to  price  and  quality  it 
averages  higher  than  Para  rubber  from  Brazil.  As  to  specifying  Para 
rubber,  the  following  is  to  the  point. 

"  Many  consumers  do  not  appear  yet  to  understand  that  there  are  many 
other  qualities  of  rubber  besides  fine  Para,  and  that  for  many  purposes  some 
of  these  rubbers  may  be  equally  satisfactory  to,  and  in  others  more  satis- 
factory than,  pure  Para.  For  instance,  where  great  strength  and  resilience 
are  required  pure  Para  cannot  be  bettered,  but  even  in  this  regard  there  are 
certain  rubbers,  other  than  Para,  which  are  for  many  practical  purposes  suf- 
ficiently strong  and  resilient,  yet  which  are  of  decidedly  lower  price.  In  other 
instances  fine  Para  may  actually  be  less  desirable  than  a  lower  class  rubber; 
thus  in  certain  cases  it  is  desirable  to  have  a  rubber  which  contains  rather 
more  resin  than  the  fine  Para.  A  consumer,  therefore,  who,  without  refer- 
ence to  his  actual  requirements,  strives  to  pin  down  the  manufacturer  to 
fine  Para,  will  as  likely  as  not  receive  an  inferior  article  for  his  purpose 
compared  with  that  which  he  might  have  had  if  he  had  given  the  manu- 
facturer a  free  hand  in  this  regard.  It  may  be  inferior  for  a  variety  of 


METHOD  OF  TESTING  FRICTION 


35 


reasons.     In  the  first  place  Para  may  be  unsuitable  for  the  article,  or  the 

high  price  of  Para  may  conduce  to  an  inclusion  of  an  excessive  amount  of 

mineral  matter,  not  to  speak  of  remade  rubber  or 

rubber  substitutes,  in  the  article.     Again,  the  term 

'  best  rubber '  may  mean  anything  or  nothing.    A 

consumer  may  thereby  mean  Para   or  merely  rub- 
ber  unmixed   with   any   other  hydrocarbon.     The 

term  '  properly  vulcanized/  which  is  used  in  many 

specifications,  is    likewise,  in  my  opinion,  an  ob- 
jectionable one,   as  it  is   capable  of  giving   rise  to 

interminable   controversies,  and   is   in  itself  a  sug- 
gestion  that    the    manufacturer  is   likely  to   shirk 

the  most  important  part  of  his  business."1 

1T  4.  A  simple  way  to  make  the  friction  test  is 

shown  in  Fig.  49:  lines  1  inch  apart  are  marked  on 

the  strip;   the  plies  are   carefully  separated  for  an 

inch  or  two  and  a  10-pound  weight  is  hung  to  the 

lower  end  of  the  strip  to    keep  it  vertical.      The 

pulling  weight  which   is   to    measure   the   friction 

pull,  whether  it  be  10,  13,  or  18  pounds  or  more,  is 

attached  to  one  ply  and  the  time  rate  at  which  it 

pulls   loose  is   noted.     The   adhesion   between  the 

last  2  plies  is  not  measured  because  in  spite  of  the 

10-pound  weight,  the  plies  will  bend  at   the   point 

of  separation  and  the  pull  will  not   be   at  180°   to 

the  plane  of  the  separating   ply.     The  long  spring 

is  to  steady  the  pull  and  prevent  jerks. 

The   time  rate  of   separation   is    an  important 

factor  in  these  tests.      It   never  varies   directly  as 

the  pull.     Up  to  a  certain  pull,  there  may  be  no  separation   at   all,,  after 

which  the  rate  increases  gradually,  then   more   rapidly,  and  finally  a  very 

small  increase  in  the  pull  causes  a 
great  change  in  the  rate  of  separation. 
Bulletin  38  Bureau  of  Standards 
1921  edition  describes  a  power-driven 
"  friction  "  testing  machine  in  which 
the  pull  required  to  separate  the  plies 
and  the  time-rate  of  separation  are 
automatically  recorded  on  a  chart. 

26  '7  Ply  Elevator  Belt  ^  Q      Thig  referg  to  the  construction 

FIG.  50.— Assembly  of  Duck  to  make  Cer-  shown  in  Fig.  50,  which  for  the  par- 
tain  Belts  according  to  Metcalf's  Speci-  ,.  _  .  .  .„  ,  ,  . 
fication.  ticular  job  illustrates  the  assembly  of 

36-inch  4-ply  conveyor  belts  and  26- 
inch  7-ply  elevator  leg  belts.     The  point  aimed  at  in  the  conveyor  belt  is 
to  avoid  longitudinal  seams  at  places  where  the  belt  bends  on  the  trough- 
1  From  "Rubber,"  by  Philip  Schidrowitz,  Ph.D.,  F.  C.  S.,  London  1911,  pp.  292-3. 


FIG.  49.— Test  of  Quality 
of  Friction  Rubber  by 
Determining  the  Rate 
of  Separation  of  Plies 
under  a  Given  Weight. 


a 


36"  4  Ply  Conveyor  Belt 


36  BELTS  AND  BELT  MANUFACTURE 

ing  idlers;  there  are  no  joints  in  the  inside  plies  and  those  in  the  outside 
ply  are  about  3  inches  from  the  edge  where  no  bending  ever  occurs.  In  the 
elevator  leg  belt  the  seams  are  kept  away  from  the  edges  and  also  from  the 
middle  where  the  belt  bends  on  the  crown  of  the  pulleys.  Belt-makers  have 
been  known  to  make  up  the  width  of  the  inside  plies  of  belt  by  assembling 
narrow  strips  which  would  otherwise  be  waste  from  the  cutting  operation. 
Such  belts  will  not  trough  without  cracking.  At  one  of  the  Western 
smelters  a  heavy  42-inch  belt  failed  by  longitudinal  cracking  after  a  few 
months'  use.  Examination  showed  that  all  the  inner  plies  were  of  the  full 
width  of  the  belt,  but  the  wrapper  which  formed  the  two  outside  plies  was 
butted  at  a  place  which  happened  to  come  over  the  gap  between  two  pulleys 
of  the  troughing  idlers.  This  gap  was  1|  inches  wide.  The  point  of  weak- 
ness in  the  outside  ply  localized  the  bending  there;  the  belt  sagged  into  the 
gap,  was  jammed  between  the  pulleys  and  was  ruined. 

1f  7.  A  rubber  cover  A  or  A  inch  thick  is  the  standard  minimum  for 
rubber-covered  belts. 

If  8.  "  Shop  splices  "  refers  to  piecing  the  duck  end  to  end  in  making 
up  the  belt.  Piecing  is  done  to  use  the  duck  economically  and  because  the 
strips  as  received  from  the  duck  mill  are  never  over  550  feet  long  in  the 
roll.  A  butt  splice  in  a  ply  close  to  a  field  joint  might  prevent  making  a  good 
step-splice  or  it  might  pull  loose  under  load.  Belt  specifications  have  called 
for  belts  over  550  feet  long  without  end  splices  in  the  duck,  but  with  looms 
built  as  they  are,  it  is  not  possible  to  get  the  fabric  in  such  lengths. 

mf  12  and  13.  These  paragraphs  may  have  been  necessary  in  dealing 
with  inexperienced  or  unscrupulous  manufacturers,  but  reputable  belt- 
makers  object  to  some  of  the  clauses.  The  explanation  offered  on  behalf 
of  the  specification  is  that  the  engineer  is  always  the  arbiter  and  that 
cases  calling  for  rigid  enforcement  of  these  threats  and  penalities  are  very 
rare  in  recent  years;  and  that  in  case  of  belt  failure  the  engineer  would 
decide  whether  it  came  from  poor  quality  or  an  original  defect,  or  as  a 
result  of  bad  alignment,  excessive  tension,  defective  splicing  or  some  other 
negligence  or  error  on  the  part  of  the  user. 

Strength  of  friction  is  in  itself  no  sure  index  of  the  quality  of  the  belt; 
if  it  were,  the  plies  of  a  fabric  belt  might  be  glued  together  and  show  a  very 
high  test,  but  such  a  belt  would  fail  by  cracking  of  the  glue.  In  a  similar 
way  a  belt  can  be  made  with  a  rubber  friction  compound  that  will  show  a 
high  test  when  fresh  but  which  will  not  keep  its  strength  six  months.  For 
instance,  a  low-grade  friction  "doped"  with  rosin  or  shellac  may  show  18  pounds 
when  fresh,  but  less  than  10  pounds  when  ten  months  old.  Then,  too, 
the  adhesion  of  the  friction  depends  upon  care  in  manufacture  as  well  as 
on  the  inherent  strength  of  the  rubber  compound.  The  openness  of  the 
weave  of  duck,  the  degree  of  twist  in  the  threads,  the  percentage  of  moisture 
in  the  duck  when  the  rubber  is  pressed  into  it,  the  freshness  of  the  frictioned 
surfaces  when  pressed  together,  the  freedom  of  these  surfaces  from  dust 
and  the  pulverized  soapstone  so  freely  used  in  rubber  factories — all  these 
factors  are  under  control  in  the  best  establishments;  but  still  all  that  the 


SPECIFICATIONS  FOR  RUBBER  BELTS  37 

manufacturer  can  hope  for- is  that  his  friction  tests  for  a  certain  duck  and 
a  certain  compound  will  fall  within  a  range  of  10  or  12  per  cent  above  or 
below  the  desired  standard.  It  would  be  better  if  specifications  permitted 
such  a  range  in  the  friction  tests*  when  a  definite  pull  is  insisted  on,  the 
only  safe  way  for  the  experienced *3and  careful  belt-maker  is  to  call  that 
figure  his  minimum  and  make  his  belt  to  average  a  few  pounds  higher. 
There  always  have  been  concerns  in  the  belt  business  with  a  reputation  to 
make  and  none  to  lose;  with  some  of  these  the  definite  specification  offers  a 
temptation  to  go  after  the  business  with  a  low  price  on  a  belt  that  may 
"  get  by  "  on  a  high  pull.  Another  circumstance  which  has  had  its  effect 
on  low  bidding  is  the  knowledge  in  the  trade  that  belts  are  usually  wanted 
soon  after  the  order  is  placed  and  when  once  in  service  they  have  more 
than  an  even  chance  of  staying  there  in  spite  of  specifications  because  a 
replacement  often  means  annoyance  and  loss  to  the  user  beyond  the  value 
of  the  belt. 

With  the  growth  of  technical  knowledge  in  the  belt  business  there  has 
come  greater  co-operation  between  makers  and  users.  Specifications  for  grain 
belts  have  been  changed  from  time  to  time  and  the  standard  of  quality  has 
been  raised.  Some  engineers  prominent  in  the  business  buy  rubber  belts  on  the 
reputation  of  the  makers  without  detailed  specifications;  others  have  written 
specifications  which  in  essentials  are  a  restatement  of  the  makers'  own  ratings 
of  their  trade-marked  belts  as  to  weight  and  strength  of  duck,  strength  of 
friction  and  make-up  of  plies. 

The  following  is  a  recent  specification  issued  by  James  Stewart  &  Co., 
Ltd.,  Chicago,  for  grain  belts  with  16-pound  friction: 

SPECIFICATIONS  FOR  RUBBER  BELTS 
JAMES  STEWART  &  CO.,  LTD. 

"  1.  Rubber  Belts. — All  belts  shall  be  made  of  several  plies  of  cotton 
duck  cemented  together  and  covered  with  rubber  compound  and  shall  be 
straight,  well  stretched  and  pressed,  first-class  quality,  of  standard  manu- 
facture and  fully  up  to  the  grade  specified.  The  elevator  leg  belts  shall  be 
6-ply;  and  conveyor  belts  shall  be  4-ply. 

"  2.  The  duck  used  in  the  construction  of  these  belts  shall  be  of  the 
best  quality  of  Mount  Vernon  or  equal  grade  of  cotton  duck.  A  piece  of 
duck  36  X42  inches  shall  weigh  not  less  than  32  ounces  for  elevator  belts 
and  not  less  than  30  ounces  for  conveyor  belts.  The  duck  for  each  belt 
shall  be  made  in  one  piece  lengthwise  without  any  other  splice  except  one 
splice  to  make  the  belt  endless  for  all  belts  less  than  450  feet  long.  The 
tensile  strength  shall  be  tested  by  pulling  a  strip  2  inches  wide  cut  from 
finished  belt  longitudinally  by  a  fair  pull  in  the  jaws  of  an  approved  testing- 
machine.  The  ultimate  tensile  strength  shall  be  at  least  320  pounds  per 
inch  wide  per  ply  for  belt  made  of  32-ounce  duck  and  shall  be  at  least  300 
pounds  per  inch  per  ply  for  belt  made  of  30-ounce  duck.  The  joints  of 
the  outside  ply  of  duck  for  the  conveyor  belts  shall  be  2  inches  from  the 


38  BELTS  AND  BELT  MANUFACTURE 

edge  of  the  belt  and  the  joints  in  the  elevator  belts  shall  not  be  nearer 
than  5  inches  to  the  edge  of  the  belt. 

"  3.  The  several  plies  shall  be  thoroughly  cemented  together  with 
first-class-quality  rubber  compound  making  such  adhesion  between  the 
different  plies  of  the  duck  that  they  will  stand  the  following  test: 

"  4.  A  strip  1  inch  wide  shall  be  cut  longitudinally  from  the  belt  and 
suspended  in  a  vertical  position  by  attaching  the  upper  end  to  a  hook  and 
fastening  a  10-pound  weight  to  the  lower  end.  The  various  plies  will 
then  be  pulled  off  one  at  a  time;  first,  separating  the  ply  for  a  distance  of 
2  inches  and  then  attaching  a  16-pound  weight  to  the  ply,  a  coil  spring 
scale  being  placed  between  the  weight  and  the  ply  tested.  Under  the 
above  conditions  the  separation  of  friction  must  not  be  faster  than  at 
a  uniform  rate  of  1  inch  in  one  minute.  The  cement  compound  when 
pulled  apart  shall  show  there  is  ample  rubber  in  the  composition  to  insure 
lasting  quality,  and  it  shall  also  show  a  long,  fibrous,  clinging  adhesion  to 
the  duck. 

"  5.  The  outside  covering  shall  be  a  coat  of  rubber  not  less  than  A  of 
an  inch  thick,  evenly  put  on,  thoroughly  vulcanized  and  finished  and 
shall  stand  the  following  test:  The  outer  ply  shall  be  stripped  from  the 
belt  and  bent  over  flat  on  itself  with  the  rubber  cover  outside  and  a  second 
bend  made  at  right  angles  to  the  first  bend.  The  cover  shall  be  so  elastic 
and  so  tough  that  no  cracks  shall  appear  anywhere  on  the  surface  when 
the  outer  ply  is  pressed  as  hard  as  possible  between  the  thumb  and  finger. 

"  6.  Samples  of  each  kino!  of  belt  3  feet  long  and  of  full  width  and  a 
sample  of  each  weight  of  duck  42  X36  inches  shall  be  furnished  after  order 
is  placed.  These  samples  will  be  held  by  the  engineer  to  compare  with  the 
belts  when  delivered  and  if  they  are  not  equal  they  will  be  subject  to 
rejection. 

"  7.  The  belts  furnished  shall  be  equal  to  or  superior  to  these  specifica- 
tions and  the  samples  submitted. 

"  8.  The  manufacturer  shall  furnish  experts  and  tools  and  shall  splice 
the  conveyor  belts  with  even  step  splices  in  place  thoroughly  cemented  and 
stitched  together  under  the  direction  of  the  engineer. 

"9.  Elevator  belts  shall  be  punched  by  manufacturer  for  bucket  holes 
in  rows  across  the  belt  at  right  angles  to  the  length  of  the  belt  as  shown  on 
the  detailed  drawings." 

Comment  on  Stewart's  specifications : 

If  1.  "  First-class  quality  "  should  be  qualified  by  "  for  the  purpose 
intended."  Sixteen-pound  friction  test  represents  an  advance  beyond  the 
old  standard  13-  or  14-pound  test,  but  some  recent  belts,  notably  those 
for  the  Pennyslvania  Railroad  Co.'s  5,000,000-bushel  Elevator  No.  3  at 
Baltimore,  have  been  made  to  test  still  higher,  i.e.,  20  pounds,  not  that  the 
higher  grade  of  friction  adds  any  useful  physical  quality  to  the  belt,  but 
that  it  will  keep  its  "  life  "  longer.  Belt-makers  consider  that  with  proper 
care  a  belt  with  16-pound  friction  should  average  over  ten  years  in  grain 
service  before  the  rubber  loses  its  "  life  "  and  the  belt  fails  by  separation 


SPECIFICATIONS  FOR  RUBBER  BELTS  39 

of  the  plies;  belts  with  lower-grade  frictions  are  not  expected  to  last  so 
long,  but  a  belt  with  20-pound  friction  should  last  twenty  years  or  more, 
barring  accident  or  abuse. 

•  ^[2.  The  Goodyear  Tire  and  Rubber  Co.  makes  the  following  statement 
as  to  tensile  tests  of  finished  belt :      ^ 

"  Many  methods  for  testing  finished  belts  permit  the  breaking  of  the 
sample  to  occur  in  the  jaws  of  the  testing-machine  and  are,  therefore,  not 
fair  to  the  sample.  To  obviate  this,  we  have  designed  a  sample  4  inches 
wide  at  the  ends  and  constricted  to  3  inches  wide  for  a  length  of  11  inches 
in  the  middle  with  a  total  length  of  about  22  inches.  A  1-inch  radius  is 
used  where  the  constricted  part  joins  the  wider  part  for  the  jaws.  We 
combine  a  stretching  test  with  the  tensile  test  by  holding  on  the  sample  a 
load  equivalent  to  one-third  of  the  total  specified  strength  of  all  the  duck 
in  the  constricted  part  of  the  sample  for  a  period  of  five  minutes  and  then 
report  the  stretch  in  per  cent.  The  load  is  then  increased  until  the  sample 
breaks,  the  increase  being  at  the  rate  of  2  inches  per  minute. 

"  A  wide  discrepancy  is  to  be  expected  between  the  belt  strength  and 
the  duck  strength  when  tested  according  to  the  above  methods.  There 
are  three  important  reasons  for  this,  namely:  (1)  Inasmuch  as  the  Grab 
test  gives  higher  strength  test  figures  than  represent  the  true  strength  of 
the  fabric,  the  testing  of  a  belt  containing,  let  us  say,  12  inches  wide  of 
fabric  in  the  constricted  portion  will  not  show  12  times  the  strength  of 
1  inch  of  fabric  by  the  Grab  method.  (2)  In  spite  of  our  efforts  to  build 
belts  with  all  the  plies  perfectly  co-operating,  we  have  not  eliminated  this 
factor  from  our  product.  It  often  happens  that  some  of  the  plies  are 
under  slightly  more  tension  than  others  so  that  when  the  sample  is  placed 
in  the  testing-machine,  these  plies,  having  the  higher  tension,  are  broken 
before  the  other  plies  are  quite  up  to  their  maximum  tensile  strength. 
(3)  The  question  of  speed  also  enters  into  this  problem.  In  general,  in 
testing,  the  higher  the  speed,  the  higher  the  test  results  on  the  same  material. 
The  most  uniform  results  on  duck-testing  are  obtained  at  fairly  high  rates 
of  speed  which  are  not  practicable  for  the  testing  of  large  pieces  of  finished 
belt  because  the  latter  must  be  tested  in  very  large  testing-machines. 

"  We  should  also  mention  that  some  prefer  pulling  the  duck  from 
finished  belts  and  testing  the  duck  in  one  of  the  usual  manners.  In  this 
way,  very  poor  workmanship  in  obtaining  the  co-operation  of  the  various 
plies  would  not  be  discovered." 

Another  reason  for  expecting,  and  allowing  for,  some  variation  in  tests 
of  strips  cut  from  belts  of  the  same  grade,  or  even  from  the  one  belt,  is  that 
it  is  impossible  to  trim  a  test  strip  to  an  exact  width  without  cutting  through 
one  or  more  warp  threads  in  each  ply  along  the  edge  of  the  strip.  If  the 
belt  is  made  of  duck  with  24  warp  threads  per  inch,  a  2-inch-wide  test 
strip  might  have  in  each  ply  50  or  48  or  even  only  44  effective  warp  threads 
to  take  the  load.  Between  these  there  is  an  unavoidable  variation  of  12 
per  cent.  If  the  test  strip  were  3  inches  wide,  the  same  differences  in  the 


40  BELTS  AND  BELT  MANUFACTURE 

number  of  effective  threads  would  mean  a  variation  of  only  8  per  cent. 
The  wider  strip  makes  a  fairer  test. 

1f  4.  The  rate  of  ply  separation  depends,  of  course,  on  the  adhesion  of 
the  rubber  compound  to  the  duck.  A  friction  that  tests  16  pounds  will 
naturally  strip  more  slowly  than  a  13-pound  friction;  a  20-pound  friction 
on  42-ounce  duck  might  not  strip  faster  than  8  inches  in  ten  minutes. 

1f  5.  "  Outside  covering  A-inch  thick."  This  is  standard  (see  Fig.  41) 
for  the  back  cover  on  many  belts  for  coal  and  ore  and  for  top  and  back 
covers  on  grain  conveyor  belts.  There  are  standard  elevator  leg  belts 
which  have  a  "  friction  "  surface,  that  is,  no  extra  rubber  cover,  but  merely 
the  thin  layer  pressed  on  to  the  duck  in  the  calendering  process.  See 
Fig.  40. 

IT  8.  The  construction  of  a  step  splice  is  shown  in  Fig.  60. 

Other  Specifications. — Some  of  the  requirements  mentioned  in  other 
specifications  for  rubber  belt  are  as  follows: 

1.  Belts  20  inches  or   less   in  width   shall   have  only  one   seam  in  the 
cover  ply. 

2.  Belts  over  20  inches  wide  may  have  two  seams  (in  order  to  avoid  the 
use  of  duck  wider  than  the  42-inch  standard),  but  the  seams  must  not  come  in 
the  center  of  the  belt  nor  near  places  where  the  belt  bends  in  troughing. 

3.  Belts  will  be  rejected  for  defects  in  workmanship,  such  as: 

(a)  Open  seams  or  plies  not  meeting,  requiring  a  narrow  filler  strip 

to  close  the  gap. 

(b)  Blisters   between   plies    or   under   the   covers,    repaired   or   not 

repaired.     (These  may  be  due  to  moisture  in  the  duck  at  the 
time  of  vulcanizing.) 

(c)  Rubber  cover  torn  off  edges  of  belt  (careless  handling  in  manu- 

facture). 

(d)  Soft  edges,  i.e.,  outer  plies  not  backed  up  by  inner  plies. 

(e)  Cover  ply  broken  by  overstretching. 

4.  Tests  to  be  made  on  finished  and  delivered  belts.     The  following 
paragraphs  refer  to  an  order  for  belts  to  be  used  in  a  sugar  refinery  for 
conveyors  and  elevators  for  raw  and  refined  sugar  and  for  barrel  elevators. 

"  Friction. — A  1-inch-wide  sample  will  be  cut  crosswise  from  the  belt, 
the  cover  opened  at  the  seam  and  each  ply  tested  singly  as  to  its  union  with 
the  next  ply  by  measuring  the  rate  of  separation  caused  by  a  weight  of 
14  pounds  hanging  freely  to  the  upper  end  of  the  ply  under  test,  as  the 
sample  hangs  against  a  wall.  The  rate  of  separation  must  not  exceed 
6  inches  in  ten  minutes  for  any  one  ply  nor  average  more  than  4  inches  in 
ten  minutes  for  all  the  plies." 

"  Belts  Spliced  Endless  by  the  Manufacturer. — The  purchaser  reserves 
the  right  to  cut  across  an  endless  conveyor  belt  and  remove  a  strip  1  inch 
in  width  for  testing  purposes.  In  the  event  that  this  test  is  made  by  the 
purchaser  and  the  belt  passes  the  prescribed  requirements,  the  ends  will 
be  joined  together  by  fasteners  and  it  will  be  acceptable.  If  the  belt  fails 
to  fulfill  the  prescribed  requirements,  it  will  be  rejected,  and  it  is  mutually 


WEIGHTS  OF  RUBBER  BELTS 


41 


understood  that  the  contractor  will  have  no  claim  for  damages  against  the 
purchaser  for  damaged  belt  or  belts  due  to  the  cut." 

Location  of  Transverse  Splices  in  Duck. — The  following  paragraph  is  taken 
from  a  recent  (1922)  specification  for  48  inch  8-  and  10-ply  rubber  belts  used 
for  long  coal  conveyors.  ^ 

"  Belts  will  be  furnished  In  roll  lengths  of  approximately  500  feet  to  allow 
the  economic  use  of  duck  with  as  few  transverse  splices  as  possible.  In  no 
case  shall  there  be  any  transverse  splices  in  either  of  the  outside  plies  of  the 
belt  in  a  500-foot  roll.  When  transverse  splices  are  necessary  in  the  inside 
plies,  they  shall  be  made  by  cutting  the  ends  of  the  duck  at  45  degrees,  and 
no  two  splices  shall  be  closer  together  than  15  feet  in  the  run  of  the  belt." 

Improvements  in  Rubber  Belt  Manufacture. — The  engineering  and 
manufacturing  staffs  of  the  companies  that  make  rubber  belts  have  effected 
great  improvements  in  the  design  and  manufacture  of  the  cotton  duck,  in 
the  compounding  of  the  rubber  and  in  the  application  of  rubber  covers. 
Further  improvements  may  be  expected  in  methods  of  making  the  threads 
and  individual  fibers  of  the  cotton  thoroughly  waterproof,  and  in  bonding 
the  rubber  to  the  duck  in  such  a  way  that  the  plies  of  fabric  will  be  held 
together  more  firmly.  The  Pratt  patent  No.  1349911  of  August  17,  1920, 
describes  a  process  which  is  intended  to  accomplish  these  results.  It 
proposes  to  saturate  the  fibers  of  cotton  duck  with  a  sulfur-terpene  solution, 
then  after  evaporating  the  solvent,  to  "  friction  "  the  duck  with  rubber  in 
the  usual  way.  When  the  assembled  plies  are  vulcanized,  the  sulfur- 
terpene  compound  is  to  react  chemically  with  the  rubber  and  form  a  close 
bond  between  it  and  the  cotton  fibers. 

Weights  of  Rubber  Belts. — Most  conveyor  belts  are  built  of  28-ounce 
duck.  The  cover  on  the  pulley  side  is  about  -^V  inch  thick  on  widths  up 
to  24  inches  and  yV  inch  thick  for  wider  belts.  The  cover  on  the  carrying 
side  will  be  the  same  as  that  on  the  pulley  side  unless  it  is  ordered  thicker. 

Table  3  (Goodyear  Tire  and  Rubber  Co.)  gives  unit  weights  of  rubber 


TABLE  3.— WEIGHT  OF  FRICTIONED  FABRIC  AND  RUBBER  COVERS 
(Goodyear  Tire  and  Rubber  Co.) 


Weight  of  Frictioned  Fabric 
1  Inch  Wide,  1  Foot  Long,  1  Ply  Thick—  Pounds 

Weight  of  Rubber  Cover 
1  Inch  Wide,  1  Foot  Long 

28-Ounce 

32-Ounce 

36-Ounce 

^-Inch  Thick 

.026 

.029 

.032 

.025 

Weight  per  Square  Foot. 
Pounds  per  Ply 

Weight  per  Square  Foot. 
^-Irich  Thick 

.312 

.348 

.384 

.300 

42 


BELTS  AND  BELT  MANUFACTURE 


TABLE   4.— WEIGHT   OF   STANDARD   RUBBER   BELTS    (28-OUNCE    DUCK) 
POUNDS  PER  LINEAR  FOOT 

(B.  F.  Goodrich  Rubber  Co.) 
For  Heavier  Ducks  and  Covers,  See  Notes  Below 


Ply  of 
Belt 

Thickness 
of 
Top  Cover, 
Inches 

Width  of  Belt,  Inches 

10 

12 

14           16 

18 

20 

22 

24 

26 

3 
3 
3 
3 

ft 

1.05 
1.25 
1.65 
2.05 
1.28 
1.48 
1.88 
2.28 

1.26 
1.50 
1.98 
2.46 
1.54 
1.78 
2.26 
2.74 

1.47 
1.75 
2.31 
2.87 
1.79 
2.07 
2.63 
3.20 

1.68 
2.00 
2.64 
3.28 

1.89 
2.25 
2.97 
3.69 

NOTE   1 

4 
4 
4 
4 

| 

2.05 
2.37 
3.02 
3.65 
2.40 
2.72 
3.36 
4.00 

2.32 
2.66 
3.39 
4.10 
2.70 
3.06 
3.78 
4.50 

2.56 
2.96 
3.76 
4.56 
3.00 
3.40 
4.20 
5.00 
3.44 
3.84 
4.64 
5.44 

2.82 
3.26 
4.14 
5.02 
3.30 
3.74 
4.62 
5.50 
3.78 
4.22 
5.21 
5.98 

3.07 
3.55 
4.52 
5.47 

3.32 
3.87 
4.90 
5.92 

5 
5 
5 
5 

•h 
ft 

ft 

3.60 
4.08 
5.04 
6.00 
4.13 
4.61 
5.57 
6.54 
4.68 
5.17 
6.13 
7.08 

3.90 
4.42 
5.46 
6.50 
4.47 
5.00 
6.03 
7.08 
5.07 
5.69 
6.74 
7.68 

6 
6 
6 
6 

NOTE   2           

7 
7 

7 
7 

i 
1 



Width  of  Belt,  Inches 

28 

30 

32 

34 

36 

42 

48 

54 

60 

5 
5 
5 
5 

! 

4.20 
4.76 
5.88 
7.00 
4.82 
5.38 
6.50 
7.62 
5.46 
6.03 
7.14 
8.27 
6.08 
6.65 
7.77 
8.88 

4.50 
5.10 
6.30 
7.50 
5.06 
5.76 
6.96 
8.16 
5.85 
6.46 
7.66 
8.86 
6.53 
7.13 
8.32 
9.53 

4.80 
5.44 
6.72 
8.00 
5.51 
6.14 
7.43 
8.71 
6.24 
6.88 
8.17 
9.45 
6.96 
7.60 
8.87 
10.13 

5.10 
5.78 
7.14 
8.50 
5.85 
6.53 
7.88 
9.25 
6.73 
7.32 
8.67 
10.03 
7.40 
8.08 
9.42 
10.78 
8.16 
8.84 
10.20 
11.56 

5.40 
6.12 
7.56 
9.00 
6.19 
6.92 
8.35 
9.80 
7.02 
7.75 
9.18 
10.62 
7.82 
8.55 
9.97 
11.40 
8.64 
9.37 
10.80 
12.24 

NOTE   1 

11.70 
12.90 
15.30 
17.70 
13.00 
14.22 
16.62 
19.00 
14.40 
15.63 
18.00 
20.40 

6 
6 
6 
6 

1 

7.22 
8.06 
9.75 
11.42 
8.20 
9.04 
10.80 
12.38 
9.14 
9.96 
11.63 
13.31 
10.08 
10.92 
12.60 
14.28 

7 
7 
7 
7 

? 

9.36 
10.32 
12.23 
14.15 
10.40 
11.38 
13.30 
15.21 
11.52 
12.48 
14.40 
16.32 

10.52 
11.60 
13.76 
15.92 
11.70 
12.78 
14.95 
17.12 
12.96 
14.03 
16.20 
18.36 

8 
8 
8 
8 

i 

9 
9 
9 
9 

s 

l 

2 

NOTE 

NOTE  1.  Belts  above  the  heavy  line  are  too  thin  for  troughing  and  for  heavy  loads. 
NOTE  2.  Belts  below  the  heavy  line  are  too  thick  to  trough  properly  on  standard  idlers. 
NOTE  3.  For  32-ounce  duck  add  .003  Ib.  per  ply  per  inch  of  width. 
NOTE  4.  For  36-ounce  duck  add  .006  Ib.  per  ply  per  inch  of  width. 
NOTE  5.  For  cover  on  pulley  side  y£  inch  thick  instead  of  the  usual  yj  inch  add  .025  Ib. 
per  inch  of  width. 

FLANGED  BELTS  43 

covers  and  of  the  single  plies  of  frictioned  fabric  made  of  standard  conveyor 
belt  ducks. 

Table  4  (B.  F.  Goodrich  Rubber  Co.)  gives  weights  per  foot  of  fin- 
ished belts  with  top  covers  of  various  thicknesses.  The  last  lines  show 
the  additions  necessary  for  ducks  heavier  than  28  ounce  and  for  covers 
on  the  pulley  side  heavier  than  ^  inch. 

Weights  of  rubber  belts  of  various  makes  are  not  quite  the  same,  and 
are  subject  to  some  variation  even  in  any  one  make.  The  figures  given  in 
the  tables  are,  however,  fairly  representative  of  American  belt  manufacture. 

Weights  of  canvas  belts  are  given  in  Table  5,  page  49. 

Weights  of  balata  belts  of  38-ounce  duck  are  given  in  Table  6,  page  51. 

Flanged  Rubber  Belts. — In  the  Edison  ore  concentrating  plant  (see  p.  10) 
from  1893  to  1896  there  was  serious  trouble  from  the  lengthwise  cracking 
of  the  belts  due  to  the  steep  angle  (45°)  of  the  troughing  idlers.  When  the 
Edison  cement  plant  was  built  a  few  years  later,  no  belts  were  troughed; 
all  were  run  flat  and  some  had  light  rubber  flanges  about  f  inch  high  to 
retain  the  material.  When  these  flanged  belts  ran  through  a  tripper  or 
over  a  reverse  bend,  there  was  a  tendency  to  shear  the  edges  off  because 
the  lower  pulley  of  the  tripper  could  not  be  made  the  full  width  of  the 
belt,  but  had  to  clear  the  flanges  of  the  belt.  On  the  return  run  the  flanges 
rubbed  and  chafed  against  the  ends  of  the  idler  pulleys  which  were  narrower 
than  the  belt;  as  a  consequence,  the  flanges  were  destroyed.  Most  of  these 
belts  were  later  replaced  by  troughed  belts. 

If  the  flanges  had  been  made  stiff  and  heavy,  the  edges  of  the  belt  might 
have  been  supported  at  the  lower  pulley  of  the  tripper  and  on  the  return 
run,  but  that  construction  is  open  to  other  objections  and  is  costly. 

Flanges   (Fig.  51)   are  used  on  vanner  belts  employed  in  the  wet  con- 
centration of  metal-bearing  ores.     These  belts  are  from  4  to  6  feet  wide, 
made  2-  or  3-ply  with    rubber   flanges  about 
f  or  1  inch  high;    they  run  over  end  pulleys 
only  12  or  14  inches  in  diameter  and  about  10 
feet  centers.      The  speed  is  slow,  usually  less 
than  5  feet  per  minute  and  the  load  is  light, 
being  merely  a  bed  of  water  and  ore  about 
or  5  inch  deep.     The  stretch  at  the  edge  of  a 

|-inch  flange  in  going  halfway  round  a  12-inch  FlG'  *L1TF1"f?d  I5df  °f  Van" 

J.  ner  Belt  used  in  Wet  Concen- 

pulley   is  4£    inches    in    18    inches,    and    the     tration  of  Ores, 
rubber    must    be    of    very    good    quality    to 

withstand  it.  To  strengthen  the  flange  at  the  base,  to  prevent  it  from 
cracking  there,  and  to  prevent  cracks  from  extending  too  far  in  from  the 
top  edge,  vanner  belt  flanges  have  been  reinforced  by  the  insertion  of  a 
flexible  cord  of  pure  rubber,  or  an  insertion  of  fabric,  or  by  running  the 
plies  of  fabric  from  the  body  of  the  belt  up  into  the  flanges.  Church, 
in  1914,  patented  a  vanner  belt  with  flanges  detachable  for  repairs. 

Flanged  belts  have  also  been  used  in  ore-reduction  plants  to  carry  wet 
concentrates,  the  idea  being  that  a  troughed  belt  would  not  hold  the  wet 


44  BELTS  AND  BELT  MANUFACTURE 

and  semi-fluid  material  so  well  and  would  be  apt  to  spill.  In  some  of 
these,  as  in  the  Edison  plant,  the  support  of  the  return  belt  gave  trouble 
even  when  separate  grooved  idlers  were  used  at  the  ends  of  the  return 
pulleys,  to  support  the  flanged  edges.  Conveyors  of  this  kind  have  no 
real  advantage  and  they  are  seldom  used  now;  a  troughed  belt  of  the 
proper  width  and  properly  fed,  works  better  than  a  flanged  belt,  and  the 
cost  for  equal  quality  is  considerably  less,  maintenance  costs  less  and  since 
the  parts  are  not  special,  repairs  can  be  made  with  less  delay. 

In  a  vanner  belt  the  carrying  surface  must  be  flat  by  nature  of  the 
process  used  in  concentrating  the  ore,  and  the  flanges  are  necessary  to 
retain  the  layer  of  ore  and  water;  the  flanges  are  always  troublesome, 
however,  and  they  should  not  be  used  on  belts  used  solely  to  convey  material. 

Patents  have  been  granted  on  a  number  of  devices  to  increase  the 
carrying  capacity  of  a  flat  belt  by  turning  up  or  flanging  its  edges,  but 
none  has  come  into  commercial  use.  One  of  them  (507156  of  1893)  covers 
a  belt  with  side  strips  fastened  on  by  flexible  connections  so  that  while  the 
strips  normally  lay  in  the  same  horizontal  plane  with  the  main  belt,  they 
could  be  turned  up  on  the  carrying  run  to  form  a  trough-shaped  section. 
Belts  with  sectional  overlapping  metal  flanges  have  also  been  designed. 
Ridgway,  in  1899,  patented  a  belt  with  tubular  edges  which  were  intended 
to  act  as  flanges  to  retain  material  on  the  belt. 

Effect  of  Light,  Heat  and  Age. — The  absorption  of  oxygen  by  rubber 
causes  what  is  known  as  drying  or  aging.  It  lessens  the  tensile  strength 
and  stretch  of  rubber  and  manifests  itself  by  fine  cracks  in  the  surface  of  a 
belt.  Since  the  chemical  change  goes  on  faster  in  sunlight,  it  is  advisable 
to  store  rubber  belts  in  a  dark  place  and  to  protect  them  from  direct  sunlight 
when  in  use.  At  a  mine  in  Arizona  a  belt  working  in  a  conveyor  gallery 
was  considered  worn  out  and  was  replaced  by  a  spare  belt  of  the  same  make 
which  through  carelessness  had  lain  exposed  to  the  sun  for  some  months. 
The  spare  belt  lasted  only  a  few  weeks;  it  was  removed  and  the  old  worn 
belt  was  put  on  until  a  new  belt  could  be  obtained. 

Belts  age  more  rapidly  when  they  are  exposed  to  heat  in  storage  or  when 
they  carry  hot  materials. 

Figs.  52,  53  show  the  effect  of  age  on  the  tensile  strength  and  stretch 
of  various  rubber  compounds  (not  belts).  Other  tests  reported  by  the 
Bureau  of  Standards  (Bulletin  38,  edition  of  1921)  indicate  that  compounds 
which  tested  from  1000  to  2600  pounds  per  square  inch  when  fresh  lost 
20  to  30  per  cent  in  strength  after  three  years'  storage  and  40  to  60  per  cent 
after  six  years'  storage  in  a  dark,  well-ventilated  place  at  75°  F.  The  tests 
also  show  that  while  the  nature  of  the  compounding  ingredients  has  some 
effect  on  aging,  the  effect  of  "  over-cure  "  or  "  under-cure,"  especially  the 
former,  is  much  more  marked.  These  terms  refer  to  the  longer  or  shorter 
time  during  which  the  rubber  is  held  at  the  vulcanizing  heat. 

Much  of  the  improvement  in  rubber-belt  making  in  recent  years  has  come 
as  a  result  of  a  better  knowledge  of  what  to  do  to  lessen  the  effects  of  heat, 
light  and  age. 


EFFECTS  OF  LIGHT,   HEAT  AND  AGE 


45 


2600 


0  2000 
H 

f  1800 

8 

2  1600 


1200 
00 

.2 
§  1000 

I 


400 


Gyl 


Age  in  Mouths 


FIG.  52. — Effect  of  Age  on  Tensile  Strength  of  Five  Specimens  of  Rubber  Compounds. 
(Bureau  of  Standards,  Washington,  D.  C.) 


50 


12        14        16        18 
Age  in  Months 


FIG.  53. — Effect  of  Age  on  Stretch  of  Five  Specimens  of  Rubber  Compounds. 
(Bureau  of  Standards,  Washington,  D.  C.) 


46  BELTS  AND  BELT  MANUFACTURE 

How  to  Keep  Rubber  Goods. — The  following  information  is  furnished 
by  the  B.  F.  Goodrich  Rubber  Co: 

"  No  matter  how  good  the  quality  of  rubber,  or  how  short  a  time  it  is  to 
be  kept  for  use,  it  is  worth  while  to  give  some  attention  to  storage  conditions. 
The  oxidation  of  rubber  is  promoted  by  the  presence  of  heat,  light  and  air. 
Ordinarily,  room  temperatures  are  satisfactory  except  close  to  the  ceiling 
or  in  a  room  under  the  roof.  Basement  rooms  are  preferable,  and  the 
ideal  storage  place  is  a  cool,  dark  cellar  protected  from  frost  in  winter  and 
heat  in  summer,  yet  not  too  close  to  the  heating  apparatus.  Dry  air 
deteriorates  rubber  much  more  rapidly  than  moist  air,  though  an  excess  of 
moisture  is  not  best  for  articles  like  belts  which  are  made  partly  of  fabric. 
A  cellar  storeroom  is  better  if  the  floor  or  walls  are  natural  earth,  provided 
there  is  sufficient  ventilation  to  avoid  excessive  moisture. 

"  Since  the  air  in  artificially  heated  buildings  in  winter  is  usually  exces- 
sively dry,  it  is  advisable,  where  practicable,  to  provide  some  special  means 
to  maintain  normal  humidity  in  the  storeroom.  Some  users  of  rubber 
goods  provide  humidors  in  the  form  of  closed  bins  or  boxes,  in  which  are 
kept  bricks  previously  soaked  in  water,  or  flat  trays  kept  filled  with  water. 

"  In  cases  where  it  is  not  convenient  to  provide  special  storage  arrange- 
ments, care  should  at  least  be  exercised  to  avoid  placing  rubber  belts  and 
other  rubber  goods  near  steam  pipes,  radiators,  hot-air  registers,  windows 
or  ceilings." 

CANVAS  BELTS 

Stitched  canvas  belts  used  for  elevators  and  conveyors  are  generally 
made  of  cotton  duck  that  weighs  32  ounces  per  square  yard.  It  is  more 
closely  woven  and  heavier  than  32-ounce  duck  used  for  rubber  belts  because 
the  trade  custom  is  to  rate  the  latter  by  the  weight  of  a  piece  42  inches  wide, 
1  yard  long;  on  that  same  basis,  32-ounce  canvas  belt  duck  would  be  rated 
as  37-ounce. 

There  are  various  weaves  of  32-ounce  duck,  depending  on  the  service 
of  the  belt  and  the  experience  of  the  belt-maker.  In  general,  the  warp  threads 
are  closer,  say,  28  per  inch,  than  the  filler  threads,  which  may  be  16  per  inch. 
Sometimes  the  threads  are  all  of  the  same  size,  but  some  belt-makers  prefer 
to  have  the  filler  threads  of  conveyor  belts  heavier  than  the  warp  threads  because 
they  take  most  of  the  abrasion,  and  also  to  make  a  stronger  joint,  when, 
as  often  happens,  the  belt  fastener  used  is  of  the  wrong  type  or  is  improperly 
applied.  For  fasteners  see  p.  56. 

Fig.  54  is  a  diagram  showing,  in  a  conventional  way,  the  construction 
of  a  6-ply  stitched  belt  for  elevator  or  conveyor  service.  Duck  of  the 
proper  width  is  folded  and  assembled  to  make  the  4  inside  plies  and  these 
are  stitched  together  by  rows  about  1  inch  apart.  Then  the  wrapper  or 
cover  is  added  to  make  2  more  plies  and  the  whole  belt  is  sewed  again; 
this  time  the  stitches  are  in  rows  £  inch  apart.  The  thread  is  a  strong 
cotton  twine,  heavier  than  the  warp  or  filler;  the  lockstitch  between  the 
needle  thread  and  the  bobbin  thread  of  the  sewing-machine  is  buried 


CANVAS  BELTS  47 

within  the  thickness  of  the  belt  (see  Fig.  54)  and  it  is  not  likely  to  come 
loose  even  when  the  threads  are  worn  away  on  either  side  of  the  belt.  In 
that  respect  the  sewing  is  like  that  wjiich  fastens  on  the  sole  of  a  shoe;  the 
sole  is  held  on  even  after  the  exposed  stitches  have  been  worn  away. 

The  next  process  with  some  make's  is  to  subject  the  assembled  plies  to 
a  combination  of  pressing  and  stretching,  after  which  the  belt  is  immersed 
in  the  waterproofing  compound.  It  is  then  run  between  rolls  to  squeeze 
out  the  excess  of  liquid.  Some  makers  stretch  the  belt  during  this  operation, 
but  in  all  factories  the  wet  belts  are  finally  dried  and  "  cured  "  by  stretching 
them  out  in  horizontal  spans  150  feet  or  more  in  length  and  keeping  them 
under  tension  for  some  days  or  weeks  to  season.  During  this  time  the  oil 
in  the  compound  dries  or  partially  oxidizes  to  a  gum;  when  linseed  oil  is 
used,  the  gum  formed  has  less  strength  and  less  elasticity  than  rubber, 
but  it  is  proportionately  less  affected  by  light,  heat  and  age.  To  a  certain 
extent,  it  acts  like  the  oxidized  linseed  oil  which  forms  the  basis  of  floor 
linoleum,  and  when  properly  applied  and  "  cured  "'  it  gives  a  belt  much 
greater  resistance,  to  abrasion  than  the  raw  cotton  possesses.  Belts 
saturated  with  mineral  oils,  semi-drying  oils  and  other  substitutes  for 

•  Inside  Stitching                                                       o=Filler  Threads 
/ Putside  Stitching  / 

Warp  Threads  of 
4-Inside  Plies 

Warp  Threads  of 
2- Outside  Plies 


FIG.  54. — Diagram  Showing  Assembly  of  a  6-ply  Stitched  Canvas  Belt. 

linseed  oil  are  more  flexible,  but  they  do  not  resist  wear  so  well  and  are 
more  likely  to  stretch  in  service.  Belts  that  are  not  maintained  under 
stretch  in  the  factory  long  enough  to  dry  or  set  the  oil  properly  will  also 
show  excessive  stretch  and  a  shorter  life.  The  thicker  the  belt,  the  longer 
it  should  be  cured ;  a  good  8-ply  belt  may  be  kept  under  stretch  for  several 
months  before  it  is  considered  ready  to  use.  The  output  of  a  belt  factory 
can  be  increased  and  the  cost  of  the  product  decreased  by  shortening  the 
time  of  "  cure,"  but  it  is  apt  to  be  at  the  expense  of  quality  in  the  belt. 

Saturating  compounds  for  canvas  belts  are  of  various  kinds  depending 
on  the  work  of  the  belt. 

Class  1. — Drying  Compounds.  Belts  for  ordinary  elevator  and  conveyor 
service  are  generally  soaked  in  a  thin  oil  compound,  the  basis  of  which  is 
linseed  oil.  It  is  thin  enough  to  penetrate  all  the  fibers  of  cotton  in  the 
belt  and  after  the  excess  has  been  squeezed  out,  a  definite  quantity  of  it 
remains  in  the  fibers  to  waterproof  them  to  a  certain  degree,  to  lessen  the 
wear  due  to  internal  bending  and  friction  and  when  properly  "  cured  " 
to  make  the  threads  of  warp  and  filler  tougher  and  more  resistant  to  abrasion. 
Such  belts  are  then  coated  with  a  paint  made  of  drying  oil  and  a  mineral 
pigment;  this  fills  up  the  stitching  holes  and  when  dry,  gives  the  stitching 


48  BELTS  AND  BELT  MANUFACTURE 

twine  and  the  outside  plies  of  the  belt  a  tough  hard  surface.  This  surface 
coat  also  gives  the  belt  a  good  coefficient  of  friction  for  contact  with  the 
pulley  and  it  prevents  the  saturating  liquid  remaining  in  the  cotton  fibers 
from  drying  out  during  the  life  of  the  belt.  Belts  treated  with  Class  1 
compounds  are  not  suitable  for  working  in  the  wet,  or  under  great  heat, 
nor  where  they  are  subject  to  acid  or  alkali  dust  or  fumes. 

Class  2. — What  are  known  as  asphalt  compounds  are  mixtures  of 
asphalt  or  gilsonite  with  various  oils  and  gums.  They  make  a  belt  that 
withstands  water,  heat  and  chemical  action,  but  one  which  does  not  resist 
surface  wear  so  well  as  those  treated  with  Class  1  compounds.  Transmission 
belts  for  high  speed  work  on  small  pulleys  are  saturated  with  compounds 
of  this  class. 

Class  3. — Colorless  waterproofing  compounds  are  used  for  belts  that 
convey  bread,  crackers  and  other  food  products,  wrapped  packages  in 
stores,  books,  fabrics,  etc.,  which  must  not  be  discolored  in  handling. 
Compounds  of  Class  1  and  Class  2  are  open  to  objection  in  this  respect. 
Class  3  compounds  leave  the  canvas  its  natural  color  and  give  sufficient 
protection  against  atmospheric  moisture;  they  do  not  give  a  belt  great 
resistance  to  the  rough  handling  of  heavy  packages  nor  to  the  actual  contact 
of  wet  material. 

Class  4. — Tasteless,  odorless  waterproofing  compounds  are  put  into  belts 
used  in  canneries  to  handle  fruit  and  vegetables.  They  contain  a  wax 
which  protects  the  cotton  against  the  action  of  fruit  acids,  and  being  light 
in  color,  they  give  the  belt  that  appearance  of  cleanliness  which  is  desired 
in  canneries.  The  compound  is  not  affected  by  hot  water  or  steam  which 
is  used  in  cleaning  such  belts  to  keep  them  sanitary. 

Stitched  Canvas  Belts  for  Conveyors. — Canvas  belts  for  handling  bulk 
materials  and  heavy  packages  are  generally  treated  with  a  Class  1  compound 
(see  p.  47),  and  when  properly  made  they  stretch  no  more  than  a 
rubber  belt  and  possess  considerable  resistance  to  cutting  and  abrasion. 
This  resistance  is  less  than  that  of  a  belt  with  a  rubber  cover,  but  the 
canvas  belt  is  homogeneous  while  the  rubber  belt  is  not.  The  cover  and 
the  friction  rubber  in  a  rubber  belt  protect  the  raw  cotton  duck  from  wear, 
and  when  the  wear  has  gone  through  the  cover  and  into  the  duck,  the  plies 
are  held  together  only  by  the  tenacity  of  the  friction  gum.  This  rubber 
deteriorates  on  exposure  to  the  air  and  the  raw  cotton  is  liable  to  decay  from 
the  action  of  moisture  and  dirt.  In  a  properly  treated  fabric  belt,  the 
whole  thickness  is  equally  resistant  to  abrasion,  the  plies  are  held  together 
by  stitching,  which  is  to  a  certain  extent  effective  even  when  the  outer  plies 
are  worn  away,  and  the  threads  and  fibers  of  the  duck  do  not  mildew  from 
the  absorption  of  moisture,  as  raw  cotton  does.  When  the  cover  of  a  rubber 
belt  and  its  first  friction  layer  are  worn  away,  it  approaches  the  end  of  its 
life,  but  a  canvas  belt  is  intended  to  expose  its  whole  thickness  to  wear, 
and  it  should  bear  the  loss  of  several  of  its  plies  before  it  is  discarded. 

Protective  Mineral  Coating. — It  has  been  suggested  that  the  surface 
of  canvas  belts  be  protected  from  abrasion  by  a  coating  composed  of  a 


CANVAS  BELTS 


49 


mixture  of  stone  with  tar  or  asphalt.  The  difficulties  are  that  if  the  coating 
is  soft,  it  will  stick  to  the  return  idlers,  while  if  it  is  hard,  it  will  crack  and 
fall  off.  Canvas  belts  carrying  cement,  fine  crushed  stone,  etc.,  are  some- 
times treated  with  a  thin  coat  of  'non-drying  paint  or  asphaltic  material. 
Some  of  the  fine  stuff  in  j^he  material  carried  becomes  attached  to  the 
carrying  surface  and  in  certain  cases  it  forms  a  protective  layer  or  skin  which 
increases  the  life  of  the  belt. 

Flexibility  of  Canvas  Belts. — A  canvas  belt  can  be  made  as  flexible  for 
troughing  as  a  rubber  belt  of  the  same  number  of  plies  by  using  duck  with  a 
light  filler  or  by  treating  it  with  a  non-drying  compound,  or  by  using  it 
while  still  soft  and  unseasoned;  but  such  a  belt  will  not  last  long  under 
hard  work.  To  resist  abrasion  well,  a  belt  should  have  a  strong  filler  and 
the  saturating  compound  should  be  of  Class  1  with  a  high  percentage  of 
linseed  oil.  When  properly  cured  it  will  have  a  density  and  a  toughness 
that  are  a  measure  of  its  wearing  quality.  It  will  not  be  as  flexible  as  a 
rubber  belt  and  will  not  bear  troughing  so  well,  especially  in  the  narrow 
widths. 

For  weights  of  stitched  canvas  belts  see  Table  5. 

Balata  belts  are  made  of  cotton  duck  waterproofed  and  held  together 
by  balata,  a  tree-gum  brought  from  the  West  Indies  and  the  north  coast 

TABLE  5.— WEIGHT  OF  OILED  AND  PAINTED  STITCHED 
CANVAS  BELTS 

(Main  Belting  Co.) 
For  Asphalt-treated  Belts  Add  10  Per  Cent 


Width, 
Inches 

Weight  of  1  Foot  of  Belt,  Pounds 

4-Ply 

5-Ply 

6-Ply 

7-Ply 

8-Ply 

10-Ply 

12-Ply 

12 
14 
16 
18 
20 
22 
24 
26 
28 
30 
32 
34 
36 
38 
40 
42 
44 
46 
48 

1.30 
1.52 
1.73 
1.95 
2.17 

i.ea 

1.90 

1.95 
2.28 
2.60 
2.93 
3.25 

3.04 
3.42 
3.79 
4.17 
4.55 
4.93 

4.77 
5.20 
5.64 
6.07 
6.50 
6.94 
7.37 

7.05 
7.59 
8.13 
8.67 
9.21 
9.76 
10.30 
10.84 
11.38 

11.71 
12.36 
13.01 
13.66 
14.31 
14.96 
15.61 

2.17 
2.44 
2.71 
2.98 
3.25 
3.52 
3.79 
4.07 
4.34 
4.61 

2.39 
2.60 
2.82 
3.04 
3.25 
3.47 
3.69 
3.90 
4.12 
4.34 

3.58 
3.90 
4.23 

4.55 

4.88 
5.20 
5.53 
5.85 
6.18 
6.50 
6.83 
7.15 
7.48 
7.81 

5.31 
5.69 
6.07 
6.45 
6.83 
7.21 
7.59 
7.79 
8.35 
8.73 
9.11 

4.88 
5.15 
5.42 
5.69 
5.96 
6.23 
6.50 

7.81 
8.24 
8.67 
9.11 
9.54 
9.97 
10.41 

11.92 
12.47 
13.01 

NOTE. — Belts  between  Heavy  Lines  are  well  suited  to  idlers  shown  in  Fig.  67. 


50  BELTS  AND  BELT  MANUFACTURE 

of  South  America.  The  gum  is  plastic  at  212°  F.,  stronger  than  rubber  at 
ordinary  temperatures,  but  not  so  elastic.  It  does  not  absorb  oxygen 
from  the  air  to  the  extent  that  rubber  does;  hence  it  retains  its  life  and 
strength  for  a  long  time. 

The  raw  gum  is  washed,  as  rubber  is,  to  remove  dirt,  then  dried,  cut 
up  and  dissolved  in  a  liquid  solvent  which  when  applied  to  the  duck,  carries 
the  gum  into  the  threads  and  fibers  of  the  cotton.  The  duck  is  generally 
of  a  closer  weave  than  that  used  for  rubber  belts;  in  some  balata  belts  it 
weighs  28  to  32  ounces  per  square  yard,  but  as  made  for  conveyor  and  ele- 
vator service,  the  duck  in  the  best  balata  belts  weighs  38  to  40  ounces  and 
has  the  warp  (lengthwise)  threads  somewhat  heavier  than  the  filler  (cross- 
wise) threads. 

In  making  the  belt,  the  duck  is  washed  to  get  rid  of  any  oil  or  sizing 
used  in  spinning  or  weaving  the  yarn;  then  it  is  dried,  run  through  the  solu- 
tion of  gum  and  dried  again.  After  cutting  to  the  right  width,  it  is  folded, 
refolded,  and  rolled  under  pressure  while  warm  to  build  up  the  required 
thickness.  It  is  then  stretched  and  allowed  to  cool  under  strain.  This 
makes  a  dense,  strong  belt,  rather  stiff,  but  not  likely  to  stretch,  and  since 
its  fibers  are  impregnated  with  the  gum,  it  shows  a  high  resistance  to  the 
absorption  of  water  (see  Table  10).  The  gum  softens  at  120°  F.  and  the 
belt  must  not  be  used  where  it  may  get  too  hot. 

Balata  belts  have  been  made  in  Great  Britain  with  rubber  covers 
fastened  on  by  cement  and  by  rows  of  copper-wire  stitching,  but  that 
style  is  not  known  in  this  country.  They  have  been  made  here  with  a 
plastic  layer  of  gutta-percha  gum,  which  is  similar  to  balata,  rolled  on  to 
the  wearing  surface,  but  it  is  not  so  resistant  to  abrasion  as  rubber  is,  and 
cannot  be  made  so  thick.  Balata  belts  have  been  used  for  conveyor  work 
to  a  greater  extent  in  Europe  than  in  this  country;  this  may  be  attributed 
chiefly  to  the  fact  that  the  manufacture  of  rubber  belts  has  received  more 
attention  in  this  country  than  anywhere  else  and  competition  from  other 
kinds  of  belt  has  been  made  more  difficult  here  than  abroad.  In  this 
country  balata  belts  compete  with  others  more  actively  as  transmission 
belts  and  elevator  belts,  in  the  latter  service  because  of  their  great  strength 
and  freedom  from  stretch,  and  especially  in  elevating  wet  materials  like 
mineral  pulps  where  the  waterproof  quality  of  the  balata  belt  is  an  advan- 
tage. In  conveyor  service  they  do  not  trough  so  well  as  rubber  belts 
because  of  their  density  and  stiffness;  hence  they  are  better  suited  to  run 
on  shallow  troughing  idlers  or  flat  rollers  rather  than  on  three-pulley  or 
five-pulley  idlers  troughed  for  30°.  In  this  respect  they  are  similar  to 
canvas  belts  with  Class  1  impregnation. 

For  weights  of  balata  belts  see  Table  6. 

Solid-woven  Cotton  Belts. — Unlike  other  belts,  these  are  not  woven 
as  duck,  a  ply  at  a  time,  but  are  woven  in  their  full  thickness  in  looms 
built  for  the  purpose.  Layers  of  warp  (lengthwise)  threads  under  tension 
are  woven  in  with  layers  of  filler  (crosswise)  threads  to  make  the  required 
thickness  and  the  whole  mass  is  bound  together  in  the  loom  by  lines  of 


BALATA  BELTS 


51 


TABLE  6.— WEIGHT.  OF  BALATA  BELT  (38-OUNCE  DUCK) 
(R.  &  J.  Dick  Co.) 


Weight*  of"  1  Foot  of  Belt,  Pounds 

Width, 

1 

Inches 

*    I 

3-Ply 

4-Ply 

5-Ply 

6-Ply 

7-Ply 

8-Ply 

9-Ply 

12 

.83 

1.11 

1.40 

14 

.97 

1.30 

1.63 

16 

.11 

1.48 

1.85 

2.22 

18 

.25 

1.67 

2.09 

2.52 

20 

.39 

1.85 

2.31 

2.79 

3.24 

22 

.53 

2.04 

2.54 

3.06 

3.56 

24 

.67 

2.22 

2.76 

3.33 

3.88 

4.43 

26 

.80 

2.40 

3.00 

3.61 

4.20 

4.80 

5.40 

28 

.94 

2.59 

3.23 

3.88 

4.52 

5.17 

5.81 

30 

2.08 

2.77 

3.46 

4.16 

4.84 

5.54 

6.23 

32 

2.22 

2.96 

3.69 

4.43 

5.17 

5.91 

6.64 

34 

2.36 

3.14 

3.92 

4.71 

5.49 

6.28 

7.06 

36 

2.50 

3.33 

4.15 

4.99 

5.81 

6.65 

7.47 

38 

2.64 

3.51 

4.38 

5.26 

6.14 

7.02 

7.89 

40 

2.78 

3.70 

4.61 

5.54 

6.47 

7.39 

8.31 

42 

2.91 

3.88 

4.85 

5.82 

6.79 

7.76 

8.73 

binder  threads  which  pass  around  the  filler  threads  from  face  to  back  of  the 
belt.  Fig.  55  shows,  in  a  diagrammatic  way,  sections  lengthwise  and 
crosswise  of  such  a  belt.  The  binder  threads  serve  the  same  purpose  as  the 


Filler 


Binder  Threads 


LENGTHWISE  SECTION 


CROSS  SECTION 


SOLID  WOVEN  COTTON  BELT 
FIG.  55. — Diagram  Showing  Assembly  of  a  Solid-woven  Belt. 

stitching  used  in  a  canvas  belt  (see  Fig.  54) ;  without  them  the  belt  will  not 
hold  together. 

Solid-woven  belts  are  not  sold  on  specifications  as  to  size  of  threads, 
weight  of  assembled  belt  or  kind  of  weave.  They  are  known  by  various 
trade  names  and  the  thicknesses  are  designated  by  terms  which  are  some- 
what arbitrary.  Those'  belts  used  for  conveying  and  elevating  service 
have  generally  6  or  8  layers  of  warp  threads  and  for  tensile  strength  corre- 
spond to  6-  or  8-ply  canvas  or  rubber  belt. 

Table  7  and  Table  8  give  facts  about  two  makes  of  solid-woven  belt. 

Solid-woven  belts  were  made  originally  for  power  transmission  and  for 
that  purpose  they  are  oftenest  used.  When  impregnated  they  are  treated 
with  a  Class  2  waterproofing  compound  (see  p.  48)  and  are  cured  by 


52 


BELTS  AND  BELT  MANUFACTURE 


TABLE  7.— "WOOSTER"  SOLID- WOVEN  COTTON  BELTING 
(Duryea  Mfg.  Co.,  Bayonne,  N.  J.) 


Kind  of  Belt 

Average  Strength, 
Pounds  per 
Inch  Width 

Average  Weight 
per  1  Inch  Wide 
per  100  Ft.,  Pounds 

Average 
Thickness, 
Inch 

Equivalent  in 
Stitched  Canvas 
or  Rubber  Belt 

Light          

800 

11 

A  to  -^r 

4-plv 

Medium  
Heavy  

1400 
2300 

14 

17 

JtoJj 

A  to  f 

6-ply 
8-ply 

TABLE  8.— "SCANDINAVIA"  SOLID- WOVEN  COTTON  BELTING 
(Scandinavia  Belting  Co.,  New  York) 


Kind  of  Belt 

Average  Strength, 
Pounds  per 
Inch  Width 

Average  Weight 
per  1  Inch  wide  per 
100  Ft.,  Pounds 

Average 

Thickness, 
Inch 

Equivalent  in 
Stitched  Canvas 
or  Rubber  Belt 

Single  

1300 

10 

T6 

4 

Extra  stout  

2300 

15 

T6 

6  or  7 

Triple  

3000 

20 

T6 

8  or  more 

stretching  them  out  in  long  spans  in  the  way  stitched  canvas  belts  are 
treated.  As  they  come  from  the  loom  they  are  more  flexible  than  stitched 
canvas  belts,  and  with  a  Class  2  impregnation,  they  retain  that  charac- 
teristic and  hence  conform  very  well  to  the  contour  of  standard  troughing 
idlers.  They  do,  however,  lack  the  hard  surface  of  painted  canvas  belts 
and  are  not  so  tough  as  those  treated  with  Class  1  compounds;  and  in 
many  of  them  the  binder  threads  are  lighter  than  the  stitching  threads  used 
in  canvas  belts.  They  are  apt  to  stretch  more  in  service  than  rubber  belts 
and  canvas  belts,  but  they  have  a  high  coefficient  of  friction  for  contact 
with  the  driving  pulleys. 

Solid  woven  belts  are  frequently  used  without  waterproofing  for  light 
package-conveyors  in  stores  where  they  are  always  under  cover  and  not 
subject  to  changes  of  temperature  nor  to  severe  pulls.  Table  9  gives  a 
comparison  between  two  specimens  of  such  belting  and  one  stitched  canvas 
belt  as  to  stretch  and  ultimate  strength. 

"  R.  F.  &  C."  (rubber  filled  and  covered)  belts  are  made  by  the  Buffalo 
Weaving  and  Belting  Co.,  Buffalo,  N.  Y.  They  are  solid-woven  cotton 
belts  impregnated  with  a  rubber  solution  and  enclosed  in  a  rubber  cover. 
For  conveyor  work  the  top  cover  is  made  thicker  than  the  cover  on  the 
pulley  side  of  the  belt.  By  laboratory  test  they  are  more  nearly  waterproof 
than  other  kinds  of  belt  (see  p.  56). 

Strength  of  Belts. — In  a  rubber,  canvas  or  balata  belt  the  ultimate 
strength  depends  largely  on  the  strength  of  the  duck  of  which  it  is  made; 
in  a  solid-woven  belt  the  strength  varies  according  to  the  sizes  of  the  threads 
and  the  closeness  of  the  weave.  Belt  ducks  are  generally  referred  to  as 
weighing  so  much  per  square  yard,  or  per  yard  of  length  42  inches  wide, 


TESTS  OF  BELTS 


53 


TABLE  9.— TESTS  OF  SEVERAL  BELTS  OF  KINDS  USED  FOR 
PACKAGE  CONVEYORS 


Total  Load,  Pounds 

Per  Cent  Stretch  in  6|  Inches 

P 
Solid  Woven  6"  X4-Ply 

Stitched  Canvas 
6"X4-Ply 

No.  1 

No.  2 

600 
1200 
1800 
2400 
3000 
3600 
4200 
4800 
5400 
6000 
6600 
7200 

8.4 
11.3 
12.6 
14.3 
15.6 
17.0 
18.2 
18.7 
Broke  at  5330  Ibs. 

7.3 
10.1 
12.3 
13.6 
14.8 
16.4 
17.3 
18.2 
Broke  at  5230  Ibs. 

1.9 
2.7 
3.4 
4.3 
5.1 
5.8 
6.9 
7.6 
8.9 
9.5 
10.8 
Broke 

Breaking  strength  in 
pounds    per    inch 
width  per  ply  

222 

218 

300 

These  tests  were  made  in  a  50,000-pound  Riehle  Machine.  The  movement  of  the 
jaws  was  not  stopped  from  the  time  the  machine  started  until  the  belt  broke.  The 
record  of  stretch  was  taken  electrically  at  the  increments  of  load  indicated  in  the  left 
column.  Belt  specimens  were  18  inches  long,  10  inches  clear  between  jaws  of  machine. 

and  in  a  general  way,  the  heavier  the  duck,  the  stronger  it  is.  There  are, 
however,  many  different  ways  of  assembling  warp  threads  and  filler  threads 
to  make  a  duck  weigh  so  many  ounces  per  square  yard ;  a  duck  for  a  canvas 
belt  may  have  a  filler  relatively  heavier  than  in  the  same  weight  of  duck 
made  for  a  rubber  belt.  The  duck  for  a  balata  belt  can  be  more  closely 
woven  than  a  rubber  belt  duck.  It  is  therefore  not  possible  to  compare 
the  strengths  of  belts  solely  on  the  basis  of  the  weights  of  the  duck. 

For  reasons  stated  on  page  39,  there  is  no  direct  connection  between 
the  strength  of  a  finished  belt  and  the  strength  of  the  duck  as  tested  by  the 
strip  method  or  the  grab  method.  The  plies  do  not  all  take  an  equal  share 
of  the  load,  nor  is  the  load  uniformly  distributed  to  all  of  the  warp  threads 
in  the  width  of  the  belt.  The  "  friction  "  or  the  impregnation  of  a  belt 
has  an  important  influence  on  its  strength.  In  a  rubber  belt,  the  layers  of 
"  friction  "  rubber  act  as  a  support  for  the  threads,  prevent  distortion  of 
belt  structure  under  load  and  help  to  distribute  the  load  among  the  plies 
of  duck.  In  a  stitched  canvas  belt,  the  oxidized  or  gelatinized  oil  which 
fills  the  spaces  among  the  threads  acts  in  a  similar  way,  but  with  less  effect, 
because  it  is  not  so  strong  as  the  rubber.  In  a  balata  belt,  the  saturating 
gum  is  stiff  and  strong,  and  with  a  given  structure  of  duck  it  makes  a  belt 
higher  in  tensile  strength  and  less  in  stretch  than  with  other  means  of  holding 
the  plies  together.  In  the  best  impregnated  solid-woven  belts,  the  structure 


54  BELTS  AND  BELT  MANUFACTURE 

of  fabric  is  quite  dense  and  the  strength  is  high  (see  Tables  7  and  8), 
but  in  most  plain,  white,  solid-woven  belts  the  weave  is  not  so  close,  the 
threads  are  not  kept  in  place  by  an  impregnating  gum  and  consequently 
the  stretch  is  greater  and  the  breaking  strength  is  less.  Table  9  records 
tests  of  two  solid-woven  belts  not  impregnated  and  one  stitched  canvas  belt 
with  Class  1  impregnation. 

Strength  of  Rubber  Belts. — Since  no  two  makes  of  rubber  belts  are 
alike  as  to  the  weave  of  the  duck  even  for  the  same  nominal  weight,  it  is 
not  possible  to  assign  definite  strengths  to  the  belts,  considering  also  the 
contingencies  of  manufacture.  It  is  really  not  necessary  that  belts  should 
be  rated  by  their  breaking  strengths;  as  is  pointed  out  in  Chapter  V  belts 
are  seldom  strained  to  more  than  one-twelfth  or  one -fifteenth  of  their 
ultimate  strength,  and  with  most  belts,  the  factor  which  determines  their 
suitability  to  particular  service  and  their  life  in  service  is  the  amount  of 
stretch,  rather  than  the  breaking  strength. 

As  a  guide  for  determining  the  allowable  working  tensions,  the  following 
may  be  taken  as  representing  the  average  breaking  strengths  of  rubber 
belts  as  made  in  this  country,  measured  per  inch  of  width  per  ply  of  thickness : 

Belts  made  of  28-oz.  duck 300  Ibs. 

Belts  made  of  30-  or  32-oz.  duck .      325  Ibs. 

Belts  made  of  36-oz.  duck 360  Ibs. 

That  is,  a 

20-inch  5-ply  belt  of  28-oz.  duck  is  good  for  about  30,000  Ibs. 
36-inch  6-ply  belt  of  36-oz.  duck  is  good  for  about  77,000  Ibs. 

Strength  of  Fabric  Belts. — Stitched  canvas  belts  of  32-ounce  duck 
will  break  at  about  300  pounds  per  inch  per  ply. 

Balata  belts  are  made  of  various  weights  of  duck;  tests  of  the  best  grade 
using  38-  or  40-ounce  duck  show  about  400  pounds  per  inch  per  ply.  In 
general  they  are  about  20  or  25  per  cent  stronger  than  rubber  belts  of 
28-  or  32-ounce  duck. 

On  the  relation  between  ultimate  strength  and  working  tensions 
see  Chapter  V. 

For  weights  of  belts  see  Tables  3,  4,  5,  6;  7,  8. 

Various  Belts  for  Different  Kinds  of  Service. — American  practice  in 
belt-conveying  has  for  years  been  close  to  the  rubber  belt  business,  and 
more  rubber  belts  are  used  for  conveyor  work  than  belts  of  other  kinds; 
stitched  canvas,  balata  or  solid-woven  cotton  belts.  Rubber  belts  can  be 
made  to  handle  economically  material  of  all  kinds,  light  or  heavy,  fine  or 
coarse,  wet  or  dry.  For  carrying  hard  material  in  heavy  pieces  a  high-grade 
rubber  belt  with  a  good  cover  should  make  the  best  conveying  medium, 
but  it  would  not  be  economy  to  use  such  an  expensive  belt  for  carrying 
crushed  coal,  and  it  would  be  a  waste  of  money  to  use  it  on  a  package 
conveyor.  A  rubber  belt  of  medium  grade  with  a  light  cover  will  in  most 
cases  carry  small  coal  for  less  cost  per  ton  or  per  year  than  a  high-grade 


VARIOUS  BELTS  FOR  DIFFERENT  SERVICE  55 

belt,  especially  since  the  life-  of  a  belt  so  often  depends  upon  factors  external 
to  the  belt  itself  (see  Table  32,  page  197). 

In  conveyors  where  there  is  no  severe  cutting  action  from  the  impact 
of  material  at  the  loading  point,  atnd  where  the  belt  is  protected  from  the 
weather,  it  is  often  possiblejbo  use  ca&vas  belts  with  economy.  The  relative 
prices  of  canvas  belts  and  rubber  belts  depend  largely  on  the  costs  of  raw 
cotton  and  raw  rubber.  Since  these  fluctuate,  the  ratios  of  prices  are  not 
constant,  but,  in  general,  canvas  belts  cost  less  than  rubber  belts  of  equal 
width  and  ply.  No  one  thinks  that  a  canvas  belt  resists  cutting  and  abra- 
sion so  well  as  a  rubber  belt  with  a  cover,  but  when  its  lower  cost  is  consid- 
ered, it  may  be  economy  to  use  it  and  get  less  tonnage  or  a  shorter  life 
than  to  pay  much  more  for  a  rubber  belt.  On  the  other  hand,  buying 
canvas  belts  for  some  conveyors  would  be  throwing  money  away;  the 
material  may  be  too  heavy  or  too  sharp,  the  conditions  of  loading  and  dis- 
charge, lubrication,  care  and  general  oversight  may  be  so  good  that  a 
rubber  belt  will  have  a  chance  to  show  a  life  much  greater  in  proportion 
to  its  cost  than  any  other  kind  of  belt.  In  other  words,  if  a  canvas  belt 
costs  $750  and  under  the  operating  conditions  lasts  one  year,  it  is  better 
to  pay  $1000  for  a  rubber  belt  if  it  can  be  depended  upon  to  last  more 
than  sixteen  months;  but  if  the  average  life  of  the  rubber  belts  on  the 
conveyor  is  no  more  than  fourteen  months,  the  canvas  belt  is  more 
economical. 

Canvas  belts  are  sold  under  trade  names  that  tell  nothing  about  the 
make-up  of  the  duck,  the  stitching,  the  nature  of  the  waterproofing  com- 
pound, the  amount  of  stretch  taken  out  and  the  time  of  seasoning  or  curing. 
Correct  knowledge  on  these  points  is  not  widely  disseminated.  Some  of 
the  failures  of  canvas  belts  in  service  must  be  attributed  to  faulty  methods 
of  manufacture,  but  disappointments  in  service  are  sometimes  due  to  using 
the  wrong  kind  of  belt.  A  canvas  belt  bought  from  a  jobber's  stock  and  run 
over  troughing  idlers  may  be  a  failure  as  a  conveyor  belt,  although  it  might 
have  been  a  good  transmission  belt.  Conveyors  are  not  all  alike,  and  a 
belt  suited  to  one  may  last  only  a  short  time  on  another;  good  elevator 
belts  are  not  necessarily  good  conveyor  belts.  Canvas  belts  are  naturally 
denser  and  stiff er  than  rubber  belts  and  do  not  trough  so  well  on  some  idlers 
which  have  been  designed  for  use  with  rubber  belts. 

Canvas  belts  are  not  recommended  for  the  difficult  work  of  conveying 
or  elevating  sharp  ore  in  the  presence  of  water.  Oil-treated  belts  with 
Class  1  saturation  are  not  sufficiently  waterproof.  Belts  treated  with 
Class  2  compounds  are  better  in  that  respect,  but  for  continual  stretching 
and  bending  while  exposed  to  water,  as  in  a  wet  elevator  handling  mineral 
pulps,  they  do  not  resist  the  water  so  well  as  a  good  rubber  belt  or  a  balata 
belt.  They  are  also  deficient  in  resistance  to  cutting  and  abrasion  in  the 
presence  of  water  as  compared  with  other  belts. 

Much  of  what  has  been  said  in  the  preceding  paragraphs  about  canvas 
belts  applies  to  balata  belts  also.  They  are  stronger  and  stiffer  than 
rubber  belts  and  do  not  trough  well  on  multiple-pulley  idlers.  They 


56  BELTS  AND  BELT  MANUFACTURE 

have  been  used  to  advantage  in  handling  wet  sand  and  ores  in  conveyors 
equipped  with  cylindrical  or  flared  idlers  (see  p.  50). 

For  an  instance  of  a  special  use  of  canvas  or  balata  belts  see  p.  190. 

Absorption  of  Water  by  Various  Belts. — Table  10  gives  results  of 
laboratory  tests  of  the  absorptive  capacity  of  various  kinds  of  belts.  The 
specimens  were  all  4-inch  4-ply  belts  cut  5  inches  long  and  treated  alike. 
The  figures  in  the  table  may  not  show  which  kind  of  belt  absorbs  the  least 
moisture  in  actual  service  when  subjected  to  stretching  and  bending  in  the 
presence  of  water;  under  those  conditions  and  after  a  period  of  service,  the 
belt  becomes  more  pliable,  the  body  becomes  more  open,  and  the  per- 
centage of  absorption  will  be  greater  with  belts  of  all  kinds.  Nevertheless 
the  greatest  absorption  in  service  will  be  shown  by  those  belts  which  give  a 
high  percentage  in  the  laboratory  tests  and  to  that  extent  the  figures  of  the 
table  are  a  useful  guide. 

TABLE  10.— ABSORPTION  OF  WATER  BY  VARIOUS  KINDS  OF  BELT 
Four-inch,  4-Ply  Belts,  5  inches  long,  Soaked  50  Hours  in  Water  at  75°  F. 

Per  cent  of 
Weight  of  Belt 

Various  rubber  belts 4  to  10 

Standard  grade  stitched  and  painted  canvas  belts. .  .  9  to  1 1 

Cheaper  grade  stitched  and  painted  canvas  belts ...  12  to  22 

Belts  saturated  with  asphalt  compounds 3  to    4 

Untreated  cotton  belts 30  to  40 

Balata  belts 5  to    9 

Rubber-filled  and  covered  belt 2. 7(1  specimen) 

Belt  Fasteners. — A  fastener  for  a  belt  joint  must  be  strong  and  yet  so 
flexible  or  so  short  that  it  will  bend  around  the  pulleys  without  breaking 
the  belt  by  bending  it  crosswise  or  pull  apart  by  tearing  out  the  cut  ends 
of  the  belt.  A  fastener  for  a  conveyor  belt  must  also  be  flexible  crosswise 
or  be  applied  in  short  sections  so  that  the  belt  can  conform  to  the  contour 
of  the  troughing  idlers. 

Rawhide  lacing  and  the  coiled  wire  lacing  used  for  transmission  belts 
are  not  used  for  conveyor  belts.  They  do  not  make  a  closed  joint  and  as 
applied  to  fabric  belts  they  are  objectionable  because  they  transmit  the 
pull  to  the  filler  or  crosswise  threads  in  the  belt,  and  these  are  apt  to  pull 
out  when  the  lacing  holes  are  pierced  close  to  the  cut  ends  of  the  belt. 
To  avoid  pulling  out  and  to  transmit  the  pull  to  the  warp  or  lengthwise 
threads,  a  fastener  for  a  fabric  belt  should  grip  the  warp  threads  by  squeezing 
them  together  and  preferably  by  clinching  them  in  some  way. 

Fasteners  for  Conveyor  Belts. — There  are  several  styles  of  metal  fast- 
eners for  fabric  belts  used  for  conveyors  : 

1.  Steel  plates  with  split  rivets  (Fig.  56)  are  made  by  the  Conveying 
Weigher  Co.,  N.  Y.;  The  Bristol  Co.,  Waterbury,  Conn.;  Crescent  Belt 
Fastener  Co.,  N.  Y.,  and  others.  Except  in  very  thick  belts,  it  is  not 
necessary  to  punch  holes  for  the  rivets;  the  rivets,  when  driven  through  the 
belt,  compress  the  warp  threads  and  clinch  around  them. 


BELT  FASTENERS 


57 


2.  Steel  clinch  hooks  are  simpler,  consisting  only  of  a  steel  plate  with 
projecting  prongs  which  are  driven  through  the  belt  by  blows  of  a  hammer 


Upper  Side  of  Belt 
Showing  Steel  Plates 
and  Heads  of  Rivets. 


Pulley  Side  of  Belt 
Showing  Ends  of  Split 
Rivets  Spread  and  Im- 
bedded in  Belt. 


FIG.  56.— Belt  Joint  with  Steel  Plates  and  Split  Rivets. 

and  then  clinched  on  the  pulley  side.  In  the  "  Turtle  "  fastener  (Fig.  57) 
(Flexible  Steel  Lacing  Co.,  Chicago)  the  prongs  are  set  edgewise  to  the 
pull;  they  are  tapered  to  compress  the  warp  threads,  drive  easily  and  clinch 


Before  Inserting. 


View  of  Pulley  Side 
of  Belt  Showing  Prongs 
Bent  Over  and 
Clinched. 


FIG.  57. — "  Turtle  "  Belt  Fastener. 

on  the  pulley  side  of  the  belt.  The  Bristol  fastener  (Fig.  58)  is  similar 
in  construction;  the  tapered  prongs  enter  between  the  warp  threads  and 
get  a  firm  hold  by  squeezing  them  together. 


58 


BELTS  AND  BELT  MANUFACTURE 


3.  Bolted  Fasteners  are  steel  plates  with  bolts.     The  High  Duty  Belt 
Fastener  (Flexible   Steel   Lacing  Co.,  Chicago)  (Fig.  59)  is  used  only  for 
belts  |  inch  or  more  in  thickness  that  run  over  pulleys  at  least  2  feet  in 
diameter.     It  does  not  leave  the  belt  flush  on  either  side  and  hence  there  is 
noise  when  it  passes  over  idlers,  but  it  is  a  strong  fastener  for  very  heavy 

'         belts.      It   requires   the   belt    to    be 

drilled  for  the  bolts,  but  these  take 
no  shear;  the  hold  depends  upon 
the  powerful  compression  between  the 
opposite  plates  and  the  wedging 
action  of  the  conical  nuts.  The 
Jackson  fastener  is  similar  in  princi- 
ple, but  it  has  oval  cup  washers  on 
the  pulley  side  of  the  belt,  and  that 

side  of  the  joint  is  smooth  and  runs  quietly  over  the  idlers.  It  is  more 
fully  described  as  a  fastener  for  elevator  belts.  (See  p.  264  and  Fig. 
248.) 

4.  Hinge-pin  Fasteners. — "  Alligator  "  lacing  (Flexible  Steel  Lacing  Co.) 
consists  of  sections  of  sheet  steel  with  prongs  driven  into  the  belt  from 
both  faces  and  made  to  interlock  over  a  steel  or  rawhide  pin  to  form  a  hinge 
between  the  butt  ends  of  the  belt.     It  is  well  suited  to  belts  run  flat  and  for 


FIG.  58.— Bristol  Steel  Belt  Fastener. 


Upper  Side  of  Belt  Showing  Steel  Plates 
and  Conical  Nuts. 


Pulley  Side  of  Belt  Showing  Steel  Plates  with 
Square  Heads  of  Bolts  Set  Flush. 


FIG.  59.— High-duty  Belt  Fastener  for  Heavy  Belts. 

package  conveyors  where  a  close  butt-joint  is  not  essential.  The  fastener 
is  thin,  lies  close  to  the  belt  and  is  not  apt  to  damage  packages  at  loading  or 
discharge  stations. 

Sizes  of  Fasteners. — In  using  any  metal  fastener,  be  guided  by  the 
maker's  instructions  as  to  the  way  to  apply  it  and  the  proper  size  to  use 
for  the  particular  width  and  thickness  of  belt.  Some  kinds  suitable  for 
leather  belts  make  a  poor  joint  in  a  fabric  belt,  the  prongs  or  rivets  are  too 
close  to  the  cut  ends  of  the  belt  and  the  threads  pull  out.  In  using  steel 
plates  with  split  rivets,  the  rivets  must  be  of  the  proper  length  for  the 
thickness  of  belt. 


CEMENTED  AND  VULCANIZED  SPLICES 


59 


A  joint  made  by  a  metal  fastener  is  never  as  strong  as  the  body  of  the 
belt,  and  in  a  fabric  belt  it  is  a  point  of  weakness  because  it  opens  the  way  for 
the  entrance  of  moisture.  In  important  work,  the  cut  ends  of  the  belt  are 
covered  with  several  coats  of  rubber  cement  before  the  fasteners  are  put  on. 
This  hinders  water  from  getting  int^he  belt. 

Step-splices. — The  construction  of  a  step-splice  is  shown  in  Fig.  60. 
Allow  a  step  of  3  or  4  inches  for  each  ply  of  belt.  Cut  each  ply  carefully 
and  avoid  cutting  into  the  ply  below  it.  Coat  the  cut  surfaces  with  rubber 
cement,  allow  it  to  dry.  Put  on  a  second  coat,  allow  it  to  dry.  Put  on 
a  third  coat  and  when  it  is  nearly  dry  but  still  tacky,  press  the  two  ends 
of  the  belt  together  and  roll  or  beat  the  cemented  surfaces  into  thorough 
contact.  When  the  joint  is  dry,  rivet  or  stitch  the  lapped  ends  together. 

Vulcanized  Joints. — Rubber  transmission  belts  are  sometimes  made 
endless  at  the  factory  by  splicing  the  ends  and  vulcanizing  the  joint;  but 
conveyor  and  elevator  belts  are  seldom,  if  ever,  made  in  that  way,  because 
of  the  difficulty  of  getting  an  endless  belt  into  place  over  the  pulleys  and 
idlers.  Rubber  belts  for  conveyors  have  occasionally  been  made  endless, 


FIG.  60. — Ends  of  a  5-ply  Belt  Prepared  for  a  Step  Splice. 

after  being  put  in  place,  by  the  use  of  a  portable  steam-heated  vulcanizing 
clamp.  In  this  method,  a  stepped  splice  is  coated  with  a  vulcanizing  rubber 
cement,  then  squeezed  and  heated  for  some  minutes.  When  well  done  it 
makes  a  strong,  tight  joint  that  runs  quietly  over  pulleys  and  idlers  without 
clicks  and  bumps.  It  does,  however,  require  skill  and  care  to  do  the  vul- 
canizing right  and  prevent  the  formation  of  blisters  from  the  evaporation 
of  moisture  in  the  belt  near  the  clamp. 

The  expense  of  the  vulcanizing  equipment  and  the  necessity  for  skilled 
labor  will  prevent  this  method  from  coming  into  general  use,  but  these 
factors  do  not  weigh  so  heavily  in  the  case  of  an  important  installation 
that  uses  many  belts,  especially  if  the  belts  are  thick  and  hard-worked. 
Field  vulcanizing  equipments  for  such  installations  are  not  yet  made  in  a 
commercial  way,  but  it  is  probable  that  they  will  be  developed  to  that 
point  as  thick  and  heavy  belts  come  into  wider  and  more  general  use. 

Steel  Belts. — Flexible  steel  bands  are  used  in  Europe  as  conveyor  belts; 
there  are  said  to  be  over  1000  installations  in  Germany,  Sweden  and  Eng- 
land (1922).  Very  few  have  been  built  in  the  United  States.  In  1911 
one  was  installed  at  a  smelter  in  Utah;  it  was  24  inches  wide,  of  No.  14 


60 


BELTS  AND  BELT  MANUFACTURE 


gage  soft  steel  (0.08  inch  thick)  and  ran  100  feet  per  minute  over  cylindrical 
rollers  on  the  upper  run;  it  slid  back  on  the  empty  run.  The  conveyor 
was  50-foot  centers,  horizontal,  and  carried  copper  matte  shoveled  from 
railroad  cars.  The  end  pulleys  were  48  inches  diameter,  cast  iron,  not 
lagged.  The  conveyor  was  used  a  few  months,  then  scrapped.  The  trouble 
was  in  the  repeated  breakage  of  the  steel  band,  probably  from  the  blows 
from  the  matte  shoveled  onto  the  band  and  from  material  caught  between 
the  return  belt  and  the  foot  pulley.  Besides,  soft  steel  is  not  elastic  enough 
to  withstand  continual  bending  back  and  forth  over  pulleys  and  idlers. 

A  similar  steel  belt,  somewhat  wider,  was  used  in  a  foundry  in  the 
Pittsburgh  district  about  fifteen  years  ago  to  carry  molds  on  the  upper  run 
and  empty  flasks  on  the  return.  It  was  not  a  success. 

Sandvik  Belts. — This  belt,  made  at  Sandvik,  Sweden,  is  a  thin  band 
of  cold  rolled  steel  0.03  or  0.04  inch  thick,  very  flexible,  but  not  capable  of 
troughing.  It  comes  in  lengths  up  to  300  feet  and  in  widths  up  to  16  inches; 
the  makers  are  not  in  position  to  roll  wider  bands. 

European  practice  is  to  use  end  pulleys  not  less  than  40  inches  in  diameter 
and  lag  them  with  fabric  belt  or  rubber  belt  to  maintain  driving  contact, 
and  especially  to  prevent  the  fine  particles  which  adhere  to  the  band  from 
being  jammed  against  the  pulley  rim  and  causing  dents,  buckles  or  breaks 
in  the  band.  The  speed  is  never  over  300  feet  per  minute,  usually  less  than 
200  feet.  For  short  runs  and  for  materials  not  especially  abrasive,  the 
carrying  run  slides  in  a  trough  like  the  old-time  grain  conveyors  (Fig.  20). 

The  empty  run  may  slide  back  or  return  over 
idlers;  these  may  be  25  to  35  feet  apart  if 
clearance  for  the  sag  permits.  When  the 
loaded  run  cannot  be  slid,  it  is  carried  on  flat- 
faced  rollers  (Fig.  61),  12  to  18  inches  in 
diameter.  Especial  care  must  be  taken  to 
keep  pieces  of  material  from  falling  on  the 
return  belt  and  getting  between  it  and  the 
end  pulley,  or  the  thin  steel  ribbon  is  apt  to 
be  buckled  or  broken.  The  same  thing  may 
happen  if  a  hard  crust  of  material  forms  on 

the  rims  of  the  pulleys.  When  discharge  is  not  over'' the  end  pulley,  a 
diagonal  plow  or  scraper  (Fig.  149)  is  used  to  throw  material  sideways  off 
the  belt. 

All  fabric  belts,  especially  rubber  belts,  have  been  very  costly  in  Europe 
since  the  Great  War,  and  these  steel  belts  are  among  the  substitutes  used 
there,  especially  in  Germany.  They  are  light,  run  quietly  and  when  run 
on  rollers  are  said  to  take  less  power  than  fabric  belts.  The  power  required 
to  slide  the  band  in  wooden  troughs  is  said  to  be  moderate.  At  a  German 
chemical  works  a  horizontal  conveyor  115  feet  long  carrying  30  tons  of 
potash  salt  per  hour,  a  steel  band  sliding  in  a  wood  trough  at  200  feet  per 
minute  required  1$  horse-power.  The  return  belt  slid  on  wood  planks; 
these  and  the  trough  bottom  were  lubricated  with  flake  graphite.  At 


Carrying  Run 


FIG.  61.— Sandvik  Flat  Steel 
Belt  Conveyor. 


STEEL  BELTS 


61 


another  works  a  conveyor  108  feet  long  inclined  2°,  discharges  to  another 
120  feet  long  inclined  12°,  capacity  40  tons  potash  salt  per  hour  at  200  feet 
per  minute  belt  speed.  The  upper,  run  slides  in  a  wood  trough,  not  lubri- 
cated; the  empty  run  returns  oVer  rollers.  Five  horse-power  drives  the 
two  conveyors,  including  josses  in  <jk>wer  transmission  and  the  friction  at  a 
scraper  plow  used  for  discharging  the  salt. 

The  Sandvik  belts  are  used  in  Germany  chiefly  for  conveying  materials 
which  will  form  a  load  of  considerable  depth  on  the  belt  and  not  scatter 
sideways  and  spill  over  the  edge.  With  such  substances  as  raw  sugar  and 
potash  salts,  the  carrying  capacity  of  a  16-inch  belt  may  be  as  much  as  800 
cubic  feet  per  hour  per  100  feet  per  minute  belt  speed;  this  is  about  double 
the  ordinary  rating  of  a  flat  belt  with  free-flowing  material. 

When  the  upper  run  travels  on  rollers,  its  capacity  in  free-flowing  material 
is  that  of  a  flat  belt.  (See  Fig.  138.)  To  get  a  conveyor  capacity  beyond 
that  of  a  16-inch  width, 
which  is  the  present  limit 
of  manufacture,  some  con- 
veyors have  been  built  in 
Europe  with  three  parallel 
strips  run  with  their  edges 
overlapping  3  or  4  inches, 
but  not  fastened  together. 
The  outer  strips  are  driven 
by  pulleys  keyed  to  the 
head  shaft;  the  middle  strip 
lying  over  the  others  en- 
gages a  narrower  pulley  on 
the  head  shaft  driven  by 
friction  from  the  other  two. 
On  the  return  run  the  three 
strips  are  carried  separately, 
the  middle  one  on  its  own 
rollers  at  a  level  lower  than 
the  outer  strips.  Recent 
experience  with  this  three- 
piece  construction  has 
shown  it  to  be  troublesome 
in  operation,  and  it  is  not 
likely  to  be  widely  used. 

Joining  the  Ends. — To 
form  a  splice  in  the  Sandvik 
band  the  ends  are  cut  off 
square,  or  to  form  a  V  (fish- 
tail splice),  then  lapped 
about  2 1  inches  and  secured 
pitch. 


FIG.  62.— Steel  Wire  Belt  used  in  Europe  as  a  Sub- 
stitute for  Fabric  Belt. 

by   two    rows    of    A-inch  rivets    1^-inch 


62 


BELTS  AND  BELT  MANUFACTURE 


Steel  Mesh  Belts  have  been  used  in  Europe  for  sixty  years  or  more 
but  very  few  have  appeared  in  this  country.  They  consist  of  coils  of  wire' 
round  or  square,  in  cross-section,  interlaced  together  and  then  flattened' 


FIG.  63.— Steel  Belt  of  Woven  Wire  with  Fabric  Belt  Selvages. 

As  generally  used  abroad,  the  coils  are  joined  over  wire  pins  which  may  be 
bent  at  their  ends  and  interlocked  to  form  a  selvage  or  border  (Fig.  62) 
or  the  pins  may  be  connected  by  flat  links  forming  a  chain  selvage.  When 
the  coils  are  interlaced  into  each  other  with  no  joint  pins,  the  pitch  shortens 


FIG.  64.— Woven  Wire  Belt  with  Chain  Selvages. 

slightly  when  the  coils  bend  on  each  other  and  the  belt  is  more  apt  to  kink 
and  is  harder  to  handle.  For  that  reason  a  wire  strand  or  a  wire  rope  is 
sometimes  used  as  a  selvage  for  the  wide  wire  mesh  aprons  used  in  drying 


STEEL  BELTS 


63 


machines  in  this  country,  or  the  apron  may  be  held  straight  and  in  shape 
and  its  edges  protected  from  wear  from  the  tracks  on  which  it  slides  by  the 
use  of  an  edging  of  fabric  belting  as  in  the  Proctor  patent  of  1900  (Fig.  63) 
or  by  chains  along  each  edge  as  in  Fig.  64. 

Originally  wire  mesh  belts  were  used  in  England  and  Germany  to  carry 
and  drain  wet  coal  or  sugar  beets  or  to  handle  packaged  goods;  but  in  Ger- 
many since  the  war  al)  fabric  belts  are  so  scarce  and  high-priced  that  these 
wire  belts  are  used  to  carry  all  sorts  of  bulk  materials,  even  fine  stuff.  To 
lessen  the  leakage  through  such  belts  thin  strips  of  wood  or  metal  are 
inserted  in  the  flattened  coils,  or  they  are  covered  with  thin  fabric.  These 
devices  must,  however,  be  regarded  as  makeshifts.  They  are  heavy,  and 


FIG.  65. — Two  Conveyors  each  with  a  j-inch  Endless  Wire  Rope.     (Link-Belt  Company.) 

clumsy,  they  do  not  prevent  leakage  altogether,  and  there  is  always  spill 
on  the  return  run  of  the  belt. 

In  this  country  wire  mesh  belts  have  been  used  for  drying-machine 
aprons  and  in  a  few  bakeries  to  carry  and  cool  freshly  baked  bread.  Several 
United  States  patents  (for  instance,  Pattee,  1916)  have  been  issued  for 
belts  consisting  of  combinations  of  steel  tension  members  with  rubber 
filling,  or  with  layers  of  fabric.  They  are  not  made  in  a  commercial  way. 

Steel  Rope  Belts. — A  few  have  been  used  in  the  United  States.  A 
flexible  steel  rope  spliced  endless  is  laced  back  and  forth  between  a  grooved 
driving  drum  and  a  grooved  foot  drum  with  one  bend  over  a  sheave  which 
acts  as  a  tightener  and  also  leads  the  rope  from  the  top  of  one  outside  groove 
on  the  foot  drum  to  the  bottom  of  the  outside  groove  at  the  opposite  end 
of  the  drum.  As  shown  in  Fig.  65,  it  was  used  to  carry  and  cool  freshly 
baked  bread.  The  necessity  for  resplicing  the  rope  occasionally  was  an 
inconvenience,  because  few  mechanics  can  do  the  job  right.  In  later 


64  BELTS  AND  BELT  MANUFACTURE 

conveyors  built  for  the  same  purpose  multiple  strands  of  light  malleable 
iron  chain  have  been  used  instead  of  the  wire  rope. 

Hemp  Rope  Belts  made  of  a  number  of  parallel  manila  ropes  stitched 
and  sewed  together  to  a  fabric  backing  have  been  used  abroad  for  package 
conveyors.  One  was  used  as  a  baggage  conveyor  at  a  railroad  station  in 
Paris  twenty  years  ago.  The  construction  has  no  particular  merit  either 
as  to  low  cost  or  durability  in  service. 


- 

CHAPTER  IV 
SUPPORTING  AND  GUIDING  THE  BELT 

Commercial  Troughing  Idlers. — The  development  of  troughing  idlers 
has  been  described  in  Chapter  II  and  reference  has  been  made  to  a  number 
of  styles  which  embodied  various  ideas  as  to  how  an  idler  ought  to  be 
made,  but  which  have  not  survived.  Those  which  are  on  the  market 
to-day  may  be  considered  as  having  passed  the  test  of  use.  There  are, 
however,  styles  in  machinery  just  as  there  are  styles  in  dress,  and  what 
happens  to  be  in  style  this  year  may  not  be  advertised  at  all  ten  years 
hence.  Changes  are  not  always  improvements;  idlers  of  old  form  and  sim- 
ple design  are  not  necessarily  inferior  to  those  covered  by  patents  or  of 
recent  origin. 

The  original  three-pulley  two-plane  idler  shown  in  Fig.  29  is  made 


FIG.  66. — 3-pulley  2-plane  Troughing  Idler.     (Jeffrey  Mfg.  Co.) 

with  improvements,  by  several  manufacturers.  It  is  simple  and  strong, 
and  there  are  no  gaps  between  the  pulleys  where  the  belt  may  sag  and  be 
pinched.  That  is  because  the  corners  of  the  pulleys  overlap  as  regards 
the  run  of  the  belt.  As  made  by  the  Jeffrey  Manufacturing  Co.  (Fig.  66) 
the  three  pulleys  are  mounted  on  two  stands,  in  which  there  are  grease 
channels  connecting  the  inclined  shafts  with  the  horizontal  shaft.  This 
permits  two  grease  cups  to  lubricate  the  three  pulleys.  In  the  style  shown 
in  Fig.  28  (Webster  Manufacturing  Co.,  Stephens  Adamson  Manufacturing 
Co.  and  others)  the  inclined  pulleys  run  on  grease-lubricated  hollow  shafts 
carried  on  brackets  that  are  adjustable  on  the  angle  bars.  The  horizontal 

65 


66 


SUPPORTING  AND  GUIDING  THE  BELT 


pulleys  are  tight  on  their  shaft ;  the  shaft  runs  in  oscillating  bearings,  closed 
at  one  end  and  fitted  with  a  grease  cup.  This  type  of  idler  is  used  on  many 
modern  grain  conveyors. 

Idler  Pulleys  Tight  on  the  Shaft. — In  idlers  of  the  type  shown  in  Fig.  28 
the  bearings  for  the  horizontal  shaft  must  have  some  freedom  to  swivel 
horizontally  and  vertically,  so  that  the  shaft  will  be  free  to  turn,  even 
though  the  stands  should  be  improperly  set,  or  in  case  the  conveyor  frame 
should  settle  or  get  out  of  line.  This  comment  applies  to  all  return  idlers 
and  to  troughing  idlers  in  which  the  pulleys  are  fixed  to  horizontal  shafts. 

The  Main  Belting  Co.'s  three-pulley  two-plane  idler  is  shown  in  Fig.  67. 
The  horizontal  pulley  has  twice  as  much  contact  with  the  belt  as  each 
inclined  pulley,  and  the  inclination  of  the  latter  is  adjustable  to  three 
positions — 10°,  15°,  20°  (Zieber  patent,  1916).  A  wide  center  pulley  has 
several  advantages:  1st — The  belt  will  run  straighter;  2d — Since  the 


FIG.  67. — 3-pulley    2-plane    Troughing    Idler    with    Broad    Horizontal    Pulley. 

Belting  Co.) 


(Main 


horizontal  pulley  is  tight  on  the  shaft,  most  of  the  weight  of  belt  and  load  is 
carried  to  closed-end  babbitted  bearings,  and  not  to  the  bores  of  pulleys 
running  loose  on  a  shaft.  The  adjustment  of  the  inclined  pulleys  permits 
the  belt  to  be  troughed  only  as  much  as  is  necessary  to  prevent  spill  at  the 
loading  point  and  keep  material  on  the  belt.  Many  belts  carry  loads 
which  do  not  shift  on  the  belt  after  they  are  up  to  belt  speed.  In  such  cases 
the  belt  can  be  troughed  as  much  as  necessary  to  prevent  spill  or  scatter  at 
the  loading  point,  and  then  run  with  less  troughing  for  the  rest  of  the 
distance.  In  general,  the  natter  the  troughing,  the  better  for  the  belt; 
it  will  run  straighter  and  last  longer. 

This  type  of  idler  is  well  suited  to  stitched  canvas  belts  and  balata  belts; 
they  are  stiffer  than  rubber  belts  and  do  not  trough  so  well. 

Two  Planes  or  Single  Plane. — For  the  best  guiding  action,  the  belt  in 
leading  on  to  a  two-plane  idler  should  run  as  shown  by  the  arrow  in  Fig.  29; 
it  then  gets  the  guiding  and  centering  action  of  the  horizontal  pulley  before 
it  touches  the  inclined  pulleys.  This  is  of  more  importance  in  narrow  belts 


IDLERS  FOR  PICKING  AND  SORTING  BELTS 


67 


FIG.    68. — 3-pulley   Troughing   Idler   with    Independent 
Lubrication  for  Center  Pulley  (Link-Belt  Company.) 


than  in  wide  belts,  and  the"  precaution  is  often  neglected  without  particular 
harm.  So  far  as  concerns  the  life  of  the  belt  or  the  power  required  to  run 
the  conveyor,  there  is  probably  no.  difference  between  having  the  pulleys 
in  one  plane  or  two  planes. 

Single  Plane  Three-pulley  Idler^were  first  made  by  Robins  (see  Fig.  34) 
and  are  now  made  by 

nearly  all  concerns  in  the  ^    /^  •  <*™«  «*  *-.  ™<* 

belt    conveyor   business. 
They  are  listed  by  most 
manufacturers   for   sizes 
30  inches  and  less.     Pat- 
terns for   belts  up  to   48 
inches   are  in   existence, 
but    to    a    great    extent 
they   have    been    super- 
seded by  five-pulley  idlers  for  belts  wider  than  30  inches.      In  the  original 
form,  the  three-pulley  idler  had  two  grease  cups,  in  some  modern  designs, 
the  lubrication  of  the  center  pulley  is  made  more  certain  by  using  a  sep- 
arate cup  for  it  (Fig.  68)  mounted  on  one  of  the  brackets. 

In  the  Weller  Manufacturing  Co.'s  three-pulley  idler  (Howard  patent, 
1920)  (Fig.  69)  most  of  the  weight  of  belt  and  load  is  carried  on  a  broad 
center  pulley  or  pulleys  fixed  to  a  shaft  which  runs  in  babbitted  trunnion 
bearings,  each  with  its  own  grease  cup.  The  merit  of  this  construction  is 
that  the  running  friction  is  on  babbitted  journals  and  not  on  a  compara- 
tively short  hub  of  a  cast-iron  pulley  with  lubrication  that  is  sometimes 
uncertain.  The  inclined  pulleys  act  on  about  one-fourth  of  the  width  of 

the  belt  at  each  side  and  are  mounted 
so  that  their  rims  at  the  bending 
corner  come  below  the  rim  of  the  hori- 
zontal pulley;  hence  the  belt  can  not 
be  pinched  there. 

Idlers  for  Picking  and  Sorting  Belts. 


FIG.  69. — 3-pulley  Troughing  Idler  with 
Center  Pulley  Tight  on  Shaft  and  Corner 
of  Inclined  Pulley  Depressed.  (Weller 
Mfg.  Co.) 


FIG.  70. — Troughing  Idler  with  Wide 
Horizontal  Pulley  for  Picking  Belt. 


—Three-pulley  idlers  (Fig.  70)  for  this  service  (see  p.  193)  are  made  by 
several  manufacturers.  The  horizontal  pulley  is  made  wide  so  that  the 
material  can  be  carried  in  a  thin  layer  and  thus  expose  all  the  pieces  to  the 
inspection  of  the  pickers.  Spool  idlers  or  flat  rolls  with  occasional  concen- 
tration can  also  be  used  for  this  work. 


68  SUPPORTING  AND  GUIDING  THE  BELT 

Two-pulley  and  four-pulley  idlers  (see  p.  14)  are  listed  by  some  makers. 
As  compared  with  other  idlers,  they  save  in  first  cost,  but  are  apt  to  cost 
more  for  belt  renewals.  Since  they  have  no  horizontal  pulley,  the  belt  is 
more  likely  to  run  crooked  (see  p.  77),  and  with  the  gap  between  the 
pulleys  under  the  deepest  part  of  the  load  on  the  belt,  the  belt  is  always  in 
danger  of  being  squeezed  by  the  pulley  rims  and  split  lengthwise. 

Five-pulley  single-plane  idlers  are  made  by  nearly  all  concerns  in  the 
business.  Current  patents  refer  to  methods  of  making  and  assembling  the 
cast-iron  supporting  stands.  Robins  lists  these  idlers  for  all  belts  from 
12  to  60  inches,  but  other  makers  do  not  furnish  five-pulley  idlers  for  sizes 
under  24  or  30  inches. 

Five-pulley  idlers  are  generally  made  with  the  outside  pulleys  set  at 
30°  and  the  intermediates  at  15°;  the  construction  is  simple  and  the  points 
of  lubrication  can  be  reduced  to  two  cups  at  the  extreme  ends  of  the  outer 
shafts  (see  Fig.  39)  although  alternative  styles  are  made  by  Webster  with 
four  cups  (see  Fig.  71)  and  by  Link-Belt  with  five  cups  (see  Fig.  75).  Web- 


FIG.  71. — 5-pulley  Idler  with  Outer  Pulleys  Adjustable  for  "  Training  "  the  Belt. 

ster  also  makes  a  five-pulley  idler  in  which  the  outer  and  intermediate 
pulleys  on  each  side  can  be  set  slightly  out  of  line  with  the  horizontal 
pulley  (Fig.  71)  so  as  to  "  train  "  the  belt  (see  p.  80). 

The  idea  back  of  the  five-pulley  idler  is  that  it  conforms  to  the  natural 
curve  of  the  belt  without  decided  bends  and  is  therefore  not  likely  to  crack 
or  crease  the  belt,  especially  if  the  belt  is  not  homogeneous  in  cross-section. 
(See  Fig.  33.)  To  get  that  result  and  avoid  gaps  between  the  pulleys, 
the  pulley  hubs  must  be  made  short  so  as  to  leave  room  for  the  tops  of  the 
cast-iron  stands  which  take  the  shafts.  In  most  cases,  the  length  of  the 
hub  is  less  than  half  the  pulley  face;  as  a  result,  the  pulleys  are  more  apt 
to  wear  loose,  run  eccentric  and  rattle  than  pulleys  on  three-pulley  idlers 
which  have  longer  hubs.  Lubrication  of  the  five  separate  pulleys  from 
two  cups  is  less  certain  than  in  three-pulley  idlers  where  there  are  only 
three  side  outlet  holes.  So  far  as  carrying  capacity  of  the  belt  is  con- 
cerned, there  is  practically  no  difference  whether  the  belt  runs  over  three 
pulleys  troughed  at  25°  or  30°  or  five  pulleys  set  at  15°  and  30°  (see  Fig. 
137). 


SIDE-GUIDE  IDLERS 


69 


As  to  the  "  steering  effect  "  of  five-pulley  idlers,  see  p.  79. 

For  comment  on  natural  troughing,  see  p.  76. 

For  comparison  of  15°  bends  in  the  belt,  see  p.  82. 

Return  Idlers  are  always  flat-£ac"ed  pulleys  mounted  on  a  straight  shaft. 
As  made  by  Robins,  the  pulleys  fgj  belts  36  inches  and  less  in  width  are 
spaced  by  collars  along  a  fixed  hollow  shaft  through  which  grease  is  forced 
by  screw  cups  on  the  ends  of  the  shaft.  In  larger  sizes,  the  pulley  is  a 
sheet  steel  tube  tight  on  a  lyVinch  shaft  which  turns  in  grease-lubricated 
bearings.  Other  makers  furnish  return  idlers  in  all  sizes  with  the  pulleys 
tight  on  the  shaft  and  the  shaft  turning  in  babbitted  bearings,  which  in 
most  cases  are  of  the  swivel  or  trunnion  type.  It  is  always  advisable  to 
have  such  bearings  self-adjusting  so  that  the  shaft  will  turn  freely  even 
if  the  hangers  which  support  the  bearings  should  be  set  wrong  or  get  out  of 
alignment.  The  Stephens  Adamson  Manufacturing  Co.  makes  return  idlers 
with  sheet  steel  pulleys  constructed  with  recessed  heads  in  which  ball 
bearings  are  mounted  as  shown  in  Fig.  91. 

Side-guide  Idlers. — Thirty  years  ago  grooved  pulleys  were  used  to  keep 
the  belt  in  place  on  "  dish-pan " 
idlers  and  on  deeply  curved  spool 
idlers.  They  destroyed  the  edges 
of  belts  rapidly.  Flat-faced  pulleys 
were  common  use  up  to  ten  years 
ago;  now  the  style  shown  in  Fig.  72 
is  more  generally  used.  The  ends 
of  the  pulley  are  rounded  to  avoid 
cutting  the  belt  if  it  should  ride  up 
on  the  face  of  the  pulley  or  get 
under  it  as  sometimes  happens. 

Side-guide  pulleys  are  never  re- 
quired on  the  return  run  of  the 
belt  unless  the  carrying  idlers  are 
not  square  with  the  run  of  the  belt 
or  unless  the  conveyor  is  out  of 
alignment  with  its  supports. 

Spacing  of  Belt  Idlers.  —  The 
spacing  of  troughing  idlers  depends 
upon  the  weight  of  belt  and  load; 
the  heavier  the  load  the  closer  the 
supports  to  prevent  the  belt  from 
sagging  too  much.  Excessive  sag 
causes  internal  wear  in  the  belt  from  stretch  of  the  friction  rubber,  and 
wear  on  its  face  from  the  slip  of  material  as  the  belt  passes  over  each 
idler.  It  adds  also  to  the  power  required  to  drive  the  conveyor. 

Usual  Rules. — Referring  to  Table  11  and  Fig.  73,  starting  at  the  head 
end,  the  first  troughing  idler  should  be  from  3  to  5  feet  from  the  center 
of  the  head  pulley;  unless  the  belt  carries  an  extra  heavy  load,  the  material 


FIG.  72. — Side  Guide  Pulley  with  Rounded 
Edges. 


70 


SUPPORTING  AND  GUIDING  THE  BELT 


TABLE  11.— SPACING  OF  BELT  CONVEYOR  IDLERS 

(Jeffrey  Mfg.  Co.) 


Width  of 
Belt,  Inches 

Dimension  A  for  Material 

Dimension  E 

Return  Idler 
Spacing 

Not  Over 
100  Ibs.  per 
Cubic  Foot 

Over 
100  Ibs.  per 
Cubic  Foot 

Sorting  Belts 
Only 

14  to  16 
18  to  20 
24  to  30 
36  to  42 

48 

5  ft.  0  in. 
4  ft,  6  in. 
4  ft.  6  in. 
3  ft.  6  in. 
3  ft.  6  in. 

4  ft.  6  in. 
4  ft.  0  in. 
3  ft.  6  in. 
3  ft.  0  in. 
3  ft.  0  in. 

30ft. 
45  ft. 
45  ft. 
45  ft. 

10ft. 
10ft. 
10  ft. 
10  ft. 
10  ft. 

3  ft.  6  in. 
3  ft.  0  in. 
2  ft.  6  in. 

will  not  spill  as  the  belt  flattens  out  on  the  pulley.  If  the  idler  is  placed 
too  close,  the  stress  in  the  edge  of  the  belt  is  too  great.  Distance  A  for  the 
support  of  the  loaded  belt  is  based  upon  the  practice  of  several  concerns 
in  the  belt-conveyor  business. 

At  the  loading  chute  it  is  important  to  place  the  idlers  closer  together 


For  Beturu  Idlers 

FIG.  73.— Spacing  of  Belt  Idlers.    (Jeffrey  Mfg.  Co.) 

to  keep  the  belt  well  troughed  and  to  prevent  the  impact  of  material  from 
deflecting  the  belt.  If  the  belt  sags  too  much  at  the  loading  point  material 
gets  under  the  edges  of  the  chute  and  skirt-board.  Twenty-four  inches  is 
a  usual  spacing  at  the  chute.  The  heel  of  the  chute  should  be  4  or  6  inches 
ahead  of  an  idler  so  that  no  lumps  can  strike  directly  over  the  idler.  When 
the  belt  is  free  to  yield  a  little  under  impact,  it  is  not  so  easily  cut  by  sharp 
angular  lumps  of  material. 

The  distance  from  the  last  idler  to  the  foot  wheel  should  be  at  least  3  feet, 

and  a  little  more  is  better  for  the  belt.     It  should 

be  made  A  if  possible. 

The  distance  X  between  a  hump  pulley  and 

the  nearest  troughing  idler  (Fig.  74)   should   not 

be  less  than   3  feet  nor  more  than  the  regular 

spacing  A  (Fig.  73). 

Return  idlers  are  generally  spaced  8  or  10  feet 

apart.     It  is  not  proper  to  use  them   as   bend 

pulleys  (see  p.  73)  and  they  should  be  set  with  reference  to  any  floor  or 
supporting  frame  so  that  spill  from  the  underside  of  the  belt  will  not  collect 
there  and  foul  the  pulleys  of  the  idler  (see  p.  177). 


FIG.  74.  —  Spacing  of 
Troughing  Idlers  at  Hump 
Pulley. 


ELEVATIONS  OF  PULLEY  RIMS 


71 


Side-guide  idlers  are  .a  necessary  evil  with  narrow  belts  on  standard 
troughing  idlers  (see  p.  79);  for  wide  belts  which  have  a  good  guiding 
contact  with  horizontal  pulleys,  they  are  not  always  needed.  In  any  case, 
use  as  few  of  them  as  possible.  »Dimension  E,  (Table  11)  is  a  "  standard-" 
spacing  for  them,  the  first  pair  being  placed  about  15  feet  from  the  head  end. 
They  should  be  set  close  Fo  a  troughing  idler  and  just  ahead  of  it  as  regards 
the  travel  of  the  belt.  If  placed  midway  between  idlers,  the  pressure  against 
the  edge  of  the  belt  is  more  likely  to  turn  or  fold  it  over  and  thus  crack  the 
belt, 

Idler  Spacing  for  Canvas  Belts. — Table  12  gives  spacing  of  idlers  recom- 
mended for  canvas  belts. 


TABLE  12.— PULLEY  SIZES  AND  IDLER  SPACING  FOR  STITCHED 
CANVAS  BELTS 

(Main  Belting  Co.) 


Spacing  of  Idlers 

Diameter 

Diameter 

Spacing 

Belt 

Usual 

Head 

Foot 

of 

Width, 
Inches 

Plies 

Pulley, 

Pulley, 

Material 

Material 

Material 

Return 

Inches 

Inches 

50  Ibs., 

75  Ibs., 

100  Ibs., 

Idlers 

Cu.  Ft. 

Cu.  Ft. 

'   Cu.  Ft. 

12 

4 

16-18 

12 

5  ft.  0  in. 

5  ft.  0  in. 

5  ft.  0  in. 

12  ft.  0  in. 

14 

4-  5 

18-20 

12-14 

5  ft.  0  in. 

5  ft.  0  in. 

5  ft.  0  in. 

12  ft.  0  in. 

16 

4-  5 

18-20 

12-14 

5  ft.  0  in. 

5  ft.  0  in. 

5  ft.  0  in. 

12  ft.  0  in. 

18 

4-  5 

18-24 

12-18 

5  ft.  0  in. 

4  ft.  9  in. 

4  ft.  6  in. 

12  ft.  0  in. 

20 

4-  5 

24-30 

14-20 

4  ft.  9  in. 

4  ft.  6  in. 

4  ft.  6  in. 

12  ft.  0  in. 

22 

5-  6 

24-30 

16-20 

4  ft.  6  in. 

4  ft.  6  in. 

4  ft.  3  in. 

12  ft.  0  in. 

24 

5-  6 

24-30 

16-24 

4  ft.  6  in. 

4  ft.  6  in. 

4  ft.  3  in. 

10  ft.  0  in. 

30 

5-  8 

30-42 

18-30 

4  ft.  0  in. 

4  ft.  0  in. 

3  ft.  6  in. 

10  ft.  0  in. 

36 

6-  8 

36-42 

20-36 

3  ft.  9  in. 

3  ft.  9  in. 

3  ft.  6  in. 

10  ft.  0  in. 

42 

6-  8 

36-54 

24-42 

3  ft.  6  in. 

3  ft.  6  in. 

3  ft.  3  in. 

8  ft.  0  in. 

48 

6-10 

48-60 

30-42 

3  ft.  6  in. 

3  ft.  3  in. 

3  ft.  0  in. 

8  ft.  0  in. 

Elevations  of  Pulley  Rims  with  Respect  to  Troughing  Idlers. — If  the  rim 

of  a  head  pulley  is  set  tangent  to  the  line  of  the  tops  of  the  horizontal  pulleys 
in  the  idlers  there  is  considerable  stretch  at  the  edges  of  the  belt  if  the 
troughing  is  deep.  Severe  stretch  at  the  edges  tends  to  break  down  the 
bond  between  the  rubber  cover  and  the  fabric,  and  is  likely  to  cause  a 
separation  of  the  plies.  To  reduce  the  amount  of  stretch,  it  is  advisable  to 
let  the  bottom  of  the  belt  lift  slightly  in  running  onto  the  head  pulley. 
One  rule  is  to  set  the  rim  of  the  pulley  to  come  half  way  in  the  depth  of  the 
trough;  that  is,  if  the  idlers  are  such  as  to  trough  the  belt  4  inches  deep, 
the  rim  of  the  pulley  should  be  about  2  inches  above  the  top  of  the  hori- 
zontal pulleys  of  the  idlers,  as  seen  in  the  cross-section  of  the  conveyor. 

For  the  same  reason,  the  rim  of  a  hump  pulley  should  be  set  an  inch 
or  two  above  the  lines  tangent  to  the  tops  of  the  horizontal  pulleys  of  the 
idlers  on  each  side  of  the  hump. 

Since  the  belt  tension  at  the  foot  of  a  conveyor  is  generally  low,  it  is 


72  SUPPORTING  AND  GUIDING  THE  BELT 

not  necessary  to  set  the  top  of  the  foot  pulley  above  the  line  of  the  horizontal 
pulleys  of  the  idlers.  In  fact,  it  is  better  to  keep  the  rim  of  the  foot  pulley 
even  with  the  horizontal  pulleys  to  avoid  the  chance  that  the  belt  might 
lift  off  the  idlers  near  the  foot  and  be  damaged  or  cut  by  rubbing  against 
the  loading  chute  or  the  skirt-boards. 

Effect  of  Increased  Spacing.  —  If  the  sag  in  feet  of  a  loaded  belt  is 
denoted  by  H  ,  the  span  in  feet  by  S,  the  weight  of  the  loaded  belt  per  foot 
by  w  and  the  pounds  tension  in  the  belt  by  T,  then 


or  if  H  and  w  are  constant,  then  S  varies  as  -s/71,  that  is,  if  the  tension  in 
the  loaded  side  of  a  conveyor  belt  at  the  head  end  is  four  times  the  tension 
at  the  foot  end,  then  for  an  equal  amount  of  sag  between  idlers,  the  idler 
spacing  might  be  twice  as  great  at  the  head  as  at  the  foot.  Considered  by 
itself,  this  might  point  the  way  toward  a  saving  in  first  cost  of  the  conveyor 
and  some  slight  economy  in  power. 

There  is,  however,  a  more  important  factor  which  governs  the  span 
between  idlers,  that  is,  the  tendency  of  a  troughed  belt  to  flatten  out  in 
cross-section  as  shown  in  Fig.  38.  When  the  trough  flattens  there  is  a 
rearrangement  of  the  load  on  the  belt  and  a  resulting  squeeze  when  the 
belt  is  troughed  again.  The  power  required  for  this  squeeze  may  not  be 
much  as  measured  in  pounds  at  each  idler,  but  it  causes  the  friction  of  the 
material  on  itself,  and  when  it  is  repeated  one  hundred  or  more  times  per 
minute  at  each  idler,  the  waste  of  power  is  considerable.  For  instance, 
in  a  conveyor  675-foot  .centers  with  idlers  spaced  3  feet  6  inches  apart  there 
are  192  idlers,  and  at  385  feet  per  minute  travel,  a  given  cross-section  on 

oo  r 

the  belt  changes  its  shape  —  =110  times  per  minute.     Since  there  are 

3  .  5 

192  places  where  the  trough  simultaneously  flattens  out,  the  result  is  that 
in  one  minute  there  are  21,120  squeezes  exerted  on  the  belt  and  on  the 
material  on  it,  to  bring  it  back  to  troughed  form  again. 

Some  of  the  power  spent  in  troughed  belt  conveyors  goes  for  this  work. 
Where  the  spacing  is  close,  the  change  of  shape  is  not  great,  but  if  the  span 
is  too  great,  the  effect  is  to  hurt  the  belt  and  waste  power. 

Tests  to  Show  Effect  of  Increased  Spacing.2—  Tests  of  the  675-foot 
conveyor  mentioned  on  page  90  showed  that  with  a  uniform  spacing  of 
3  feet  6  inches  and  a  steady  load  of  9  tons  per  minute  or  540  tons  per  hour, 
the  amperes  varied  between  20  and  22  with  the  voltage  at  500.  These 
readings  are  equivalent  to  13.5  h.p.  and  14.8  h.p.  When  one  idler  just 
ahead  of  the  loading  point  was  removed,  making  the  span  at  that  one 
place  7  feet  instead  of  3  feet  6  inches,  the  amperes  on  numerous  tests  varied 
between  50  and  55,  with  the  voltage  at  500,  corresponding  to  33.5  h.p.  and 
37.0  h.p.  That  is,  over  20  h.p.  was  required  to  re-establish  the  troughed 

1  See  Kent's  M.  E.  Pocketbook. 

2  Communicated  to  the  author  by  Mr.  E.  C.  Auld. 


EFFECT  OF  INCREASED  SPACING  OF  IDLERS  73 

form  of  the  belt  at  that  one  point.  The  deflection  or  sag  under  load  on 
this  7-foot  span  measured  If  inches  while  the  deflection  in  the  adjacent 
3-foot  6  inch  span  measured  3^3  inch.  To  lift  9  tons  per  minute  through 
H  inch  height  takes  less  than  Tfr  h.p.;  it  seems  clear  then  that  in  this 
case  it  took  more  power  to  squeeze  the  coal  back  into  troughed  form  than 
to  convey  it  675  feet. 

These  tests  show  that  the  saving  in  cost  of  troughing  idlers  which  might 
be  effected  by  varying  the  idler  spacing  is  insignificant  as  compared  with 
the  cost  of  the  power  required  to  squeeze  the  belt  and  its  load  back  into 
trough  form  when  the  span  becomes  too  great.  Since  the  tendency  to 
flatten  out  is  greater  when  the  belt  is  deeply  troughed,  it  is  quite  evident 
that  for  a  given  spacing  of  idlers  more  power  is  required  to  carry  a  certain 
tonnage  on  a  belt  over  idlers  steeply  troughed  than  over  idlers  with  a 
smaller  angle  for  the  side  pulleys.  Carrying  the  reasoning  still  further, 
properly  supported  belts  run  flat  or  nearly  so  would  require  still  less  power, 
because  the  load  cross-section  does  not  change.  A  flat  belt  will  sag  more 
between  idlers  than  a  troughed  belt  because  it  lacks  the  stiffening  effect 
of  the  upturned  sides,  but  with  loads  based  on  one-half  the  maximum 
capacity  of  the  belt  (see  p.  144)  the  difference  is  not  much. 

From  the  fact  that  the  load  cross-section  does  not  change  on  a  flat  belt, 
it  would  be  possible  to  make  the  idler  spacing  vary  as  \/T  without  the 
loss  of  power  referred  to  above;  but  if  the  sag  of  a  flat  belt  becomes  too 
great,  there  would  be  some  disturbance  of  the  load  represented  by  the 
pile  of  material  on  the  belt  cracking  crosswise  as  it  passed  over  the  idler 
pulley.  With  ordinary  spans,  this  would  amount  to  less  than  the  dis- 
turbance caused  by  squeezing  the  material  back  into  trough  form;  never- 
theless it  indicates  one  limitation  of  the  span  of  belts  run  flat  or  slightly 
troughed. 

The  ordinary  rules  for  idler  spacing  represent  current  practice  with 
troughed  belts  on  standard  three-pulley  or  five-pulley  idlers  with  grease 
lubrication.  Since  it  is  very  desirable  to  keep  the  load  cross-section  as 
nearly  constant  as  possible,  it  is  not  wise  to  increase  the  spacing  of  ordinary 
idlers,  because  they  are  relatively  cheap,  while  the  cost  of  power  is  relatively 
high.  In  equipping  a  conveyor  with  more  expensive  idlers,  as,  for  example, 
with  roller  bearings,  there  is  some  incentive  to  use  greater  spacing;  but 
in  such  cases  the  saving  of  power  due  to  the  better  idlers  will  justify  the  use 
of  a  greater  number  of  them  in  order  to  maintain  a  constant  load  cross- 
section.  In  general,  the  advantages  are  somewhat  uncertain  when  idlers 
are  spaced  further  apart  than  is  now  customary,  on  the  other  hand;  the 
disadvantages  are  quite  certain  and  measurable. 

Supporting  Belts  at  Humps  and  Bends. — Pulleys  are  generally  used  to 
change  the  direction  of  belt  travel.  They  should  be  double-belt  straight- 
face  pulleys,  3  or  4  inches  in  diameter  for  each  ply  of  belt  (see  p.  127). 
This  applies  to  snub  pulleys  and  to  pulleys  used  to  change  the  direction  of 
the  loaded  belt  from  an  incline  to  the  horizontal,  or  on  the  return  run. 
When  the  return  belt  is  deflected  through  a  considerable  angle  in  passing 


74  SUPPORTING  AND  GUIDING  THE  BELT 

from  the  head  pulley  to  the  straight  run,  or  from  the  straight  run  to  the 
foot  pulley,  it  is  not  safe  to  use  a  standard  return  idler.  The  shaft  and  the 
pulleys  are  both  too  light  for  that  work. 

Troughing  Idlers  at  Humps. — It  is  not  proper  to  make  a  hump  bend 
over  a  standard  troughing  idler  or  even  a  group  of  them;  they  are  not 
strong  enough,  except  for  light  work  or  where  the  angle  of  bend  is  small 
There  is  another  objection  to  the  plan  of  using  troughing  idlers  at  humps — 
that  is,  the  chance  that  the  belt  may  be  injured  by  the  excessive  stretch 
at  its  edges  if  the  troughed  form  is  maintained  over  the  hump.  For 
instance,  if  a  belt  is  troughed  6  inches  deep  on  a  curve  joining  a  20°  incline 
with  a  horizontal  run,  the  length  of  the  edges  will  be  2  inches  greater  than 
the  length  of  the  part  which  lies  down  on  the  horizontal  pulleys.  To  resist 
such  deformation,  the  belt  will  tend  to  rise  off  the  horizontal  pulleys  and 
rest  only  on  its  edges.  For  the  case  stated,  the  stretch  is  2  inches,  regard- 
less of  the  radius  of  curvature  of  the  hump,  but  obviously  the  effect  on  the 


FIG.  75. — Natural  Sag  of  Belt  on  5-pulley  Troughing  Idler. 

belt  is  reduced  by  using  a  large  radius,  so  that  the  stretch  will  be  spread 
over  a  greater  length  of  belt  on  the  arc. 

When  a  belt  flattens  out  on  a  pulley  used  at  a  hump,  the  load  cross-sec- 
tion changes  and  power  is  expended  in  pushing  the  material  together  when 
the  belt  is  troughed  again.  This  loss  of  power  is  the  same  as  that  which 
comes  from  spacing  idlers  too  far  apart  (see  p.  72)  and  it  is  greater  than 
is  generally  supposed.  For  that  reason,  some  conveyors  have  been  equipped 
with  troughing  idlers  at  humps,  not  of  the  ordinary  pattern,  but  of  heavier 
construction,  and  by  using  a  number  of  them,  on  a  large  radius  of  curvature, 
the  tendency  to  stretch  the  edges  of  the  belt  is  reduced  and  there  is  less 
pressure  on  each  idler. 

Since  the  stretch  of  the  edges  of  the  belt  varies  directly  as  the  depth  of 
the  trough  it  is  clear  that  hump  bends  over  shallow  troughing  idlers  or  flared 
idlers  have  less  effect  on  the  belt  than  standard  idlers  which  turn  the  edges 
of  the  belt  up  at  30°. 

Natural  Troughing. — The  Robins  stepped-ply  belt  (p.  12)  and  the 
Ridgway  hinge-edge  belt  (p.  17)  represent  efforts  to  make  belt  contour 


NATURAL  TROUGHING 


75 


adapt  itself  to  the  contour  of  three-pulley  idlers.  The  Plummer  patent  of 
1903  (see  p.  16)  was  the  first  practical  expression  of  the  principle  of  making 
the  idler  conform  to  the  natural4*urvature  of  the  belt.  To  do  this,  Plum- 
mer proposed  to  use  multiple  pulleys  with  curved  faces  and  thus  avoid 
any  bend  in  the  belt.  The  idea  did  not  come  into  commercial  use;  it  was 
followed  by  various  designs  of  five-pulley  idlers  which  to  a  great  extent 
match  the  natural  sag  of  an  empty  belt  as  shown  in  Fig.  75. 

In  carrying  out  this  idea  it  is  not  possible  to  make  any  one  size  of  idler 
fit  the  curve  of  all  belts  because  the  flexibility  for  a  given  width  varies  with 


FIG. 76 


Fio.  77 


212019181716151413121110  987    654321    01    234    567    8   9  10  11 12  13  14  15  1617  18  1920  21 


FIG. 78 


FIGS.  76-77-78.— Natural  Sag  of  Various  Rubber  Belts.    The  Horizontal  and  Vertical 

Spaces  are  One  Inch. 

the  weight  of  duck,  number  of  plies,  the  thickness  of  the  cover  and  the 
grade  and  the  thickness  of  the  layers  of  friction  rubber.  All  that  can  be 
expected  is  to  have  the  belt  lie  in  a  natural  curve  and  avoid  sharp  bends. 
In  wide  belts,  the  natural  curve  is  generally  deeper  than  the  contour  of  the 
corresponding  width  of  idler.  Fig.  77  shows  the  natural  curvature  of  four 
belts  when  lifted  by  their  edges  until  the  middle  merely  touched  a  hori- 
zontal surface.  In  Fig.  76  the  same  belts  were  lifted  until  one-fifth  of  their 
width  rested  on  the  horizontal  surface,  this  representing  the  contact  of  a 
belt  with  the  middle  pulley  of  a  five-pulley  idler.  In  these  tests  which  were 


76  SUPPORTING  AND  GUIDING  THE  BELT 

made  by  the  B.  F.  Goodrich  Rubber  Co.,  A  represents  a  42-inch  8-ply  belt 
with  |-inch  cover;  B,  a  42-inch  7-ply  belt  with  |-inch  cover;  C,  a  30-inch 
7-ply  belt  with  |-inch  cover;  D,  a  36-inch  6-ply  belt  with  |-inch  cover. 

In  belts  narrower  than  24  inches  the  natural  sag  of  an  empty  belt  is 
generally  shallower  than  the  contour  of  the  idler,  but  when  the  thickness 
does  not  exceed  the  limits  established  by  good  practice  (see  p.  115) 
a  very  slight  pressure  on  the  edges  of  the  belt  directed  toward  the  center 
is  enough  to  make  its  curvature  match  that  of  the  idler  and  bring  the  belt 
into  proper  contact  with  the  horizontal  pulley  of  the  idler. 

Fig.  78  represents  the  results  of  tests  made  by  the  author. 

No.  1  is  a  standard  grade,  24-inch  6-ply  belt  with  |-inch  cover;  total 
thickness,  A  inch. 

No.  2  is  a  belt  of  higher  grade,  24  by  6  by  |  inches;  total  thickness, 
-Jf  inch;  it  is  a  little  stiff er  than  No.  1. 

No.  3  is  a  belt  of  extra  quality,  24  inches  wide,  5  plies  of  extra  heavy 
duck,  |-inch  top  cover  and  -g-V-inch  pulley  cover  on  the  bottom. 
It  has  also  a  layer  of  "  cider-press  "  cloth  to  form  an  anchor 
for  the  top  cover  (see  p.  24)  and  the  total  thickness  is  A  inch. 
It  is  less  flexible  than  No.  1  or  No.  2. 

No.  4  is  a  high-grade  belt  used  for  wet  hard  work  on  tailings  stackers 
on  gold  dredges  (see  p.  19).  It  is  24  by  6  by  |  inch  with 
•^j-inch  bottom-cover;  total  thickness,  \  inch. 

No.  5  is  a  high-grade  trade-marked  belt  used  on  grain  conveyors,  width, 
18-inch  4-ply;  ^-inch  thick  rubber  covers. 

In  these  five  tests  the  belts  were  lifted  by  their  edges  until  the  middle 
merely  touched  a  horizontal  surface. 

While  the  five-pulley  idler  represents  in  its  contour  a  close  approxima- 
tion to  the  natural  curve  of  a  belt  suspended  by  its  edges,  it  must  not  be 
thought  that  the  belts  shown  in  Figs.  76,  77  and  78  will  not  match  the 
contour  of  three-pulley  idlers  or  idlers  of  other  form.  As  has  been  said 
above,  it  needs  only  a  slight  pressure,  as  from  inclined 'troughing  pulleys, 
to  make  any  of  the  belts  assume  a  trough  section  much  deeper  than  those 
shown.  Any  of  these  belts  will  run  well  with  three-pulley  idlers  troughed 
at  30°  or  less. 

So  far  as  the  action  on  a  good  straight-ply  belt  is  concerned,  there  is 
little  or  no  difference  between  "  natural  troughing  "  on  five-pulley  idlers 
and  troughing  over  three-pulley  idlers  at  30°  or  less.  There  is,  however,  an 
advantage  in  five-pulley  idlers  for  stepped-ply  belts  and  belts  in  which  the 
width  is  made  up  of  narrow  strips  of  duck  (see  p.  15)  or  where  the  longi- 
tudinal joints  between  the  strips  are  not  properly  located  to  avoid  the  lines 
of  bending.  In  belts  so  made,  the  smaller  angle  of  bend  on  five-pulley 
idlers  counteracts,  to  a  degree,  the  harm  done  in  not  having  the  filler  threads 
in  the  duck  continuous  across  the  lines  of  flexure.  But,  on  the  other  hand, 
the  idler  lacks  something  in  simplicity,  durability,  rugged  construction, 
certainty  of  lubrication  and  good  guiding  action.  On  these  points  five- 
pulley  idlers  may  be  inferior  to  three-pulley  idlers  and  idlers  of  other  forms. 


WEAR  OF  PULLEY  HUBS  AND  RIMS  77 

Wear  of  Pulley  Hubs  and  Rims. — In  most  of  the  modern  three-pulley 
and  five-pulley  idlers  of  the  singlerplane  type  an  effort  is  made  to  get  the 
pulley  rims  close  together  to  avoid  pinching  or  creasing  the  belt  in  the  gap 
between  them.  (See  Figs.  39,  68,  71.)  This  distance  cannot  be  made 
too  small  for  fear  that  the  rims  of  the  pulleys  will  interfere  with  each  other 
when  wear  occurs  between  the  bosses  of  the  cast-iron  stands  and  the  hubs 
of  the  inclined  pulleys  which  rest  against  them.  Interference  between 
rims  of  pulleys  prevents  them  from  turning,  and  if  the  pulley  rims  are 
cut  through  by  the  belt  sliding  over  them,  as  sometimes  happens,  the 
belt  may  be  cut  and  damaged.  It  can  be  prevented  by  inserting  washers 
between  the  stands  and  the  pulley  hubs  before  all  of  the  rim  clearance  has 
been  taken  up  by  wear.  The  bosses  on  the  stands  are  not  usually  finished; 
although  it  is  customary  to  finish  one  end  of  each  pulley  hub.  If  the 
pulley  hubs  are  central  and  symmetrical,  the  rim  clearance  can  be  main- 
tained by  reversing  the  pulleys  when  the  hubs  are  worn  on  one  side. 

The  pulleys  of  commercial  belt  idlers  are  generally  made  as  light  as 
possible  with  rims  not  over  ^  or  A  inch  thick  so  that  they  are  lively  and 
revolve  easily,  and  are  at  the  same  time  cheap.  To  avoid  cracking  in  the 
foundry  in  cooling,  and  for  easy  shop  work  in  finishing  the  rims,  the  metal 
used  is  a  soft  gray  iron.  It  does  not  resist  wear  so  well  as  harder  iron, 
nor  is  the  finished  rim  so  hard  as  the  skin  with  which  the  pulley  comes 
from  the  sand  mold.  In  coke  conveyors  the  abrasive  dust  wears  out  the 
rims  of  pulleys,  and  hence  some  concerns  prefer  to  use  troughing  and 
return  idlers  with  no  machine  finish  on  the  rims  of  the  pulleys  but  with  the 
foundry  skin  left  on  them.  Another  step  in  the  same  direction  is  the  use 
by  some  Western  mining  companies  of  idler  pulleys  cast  of  harder  metal 
in  an  iron  chill.  The  rim  in  such  pulleys  must  be  quite  thick  to  avoid 
cracking  in  cooling.  This  adds  to  the  cost,  and  makes  the  pulley  more 
sluggish  in  rotation,  but  under  certain  operating  conditions,  where  the 
belt  carries  wet  sharp  ore,  the  longer  life  of  the  pulleys  justifies  the  greater 
expense  and  perhaps  compensates  for  some  added  wear  on  the  belt. 

Why  Belts  Run  Crooked. — Assuming  that  the  center  line  of  the  conveyor 
is  in  proper  alignment  with  the  end  pulleys,  a  flat  belt  may  run  crooked  if 
the  axis  of  the  idlers  is  not  square  with  the  run  of  the  belt,  or  if  both  edges 
are  not  under  the  same  tension,  or  if  the  belt  was  badly  made,  to  begin 
with.  But  if  the  idlers  are  set  square  with  the  travel  a  normal  belt,  run 
flat,  tends  to  run  straight.  The  evidence  on  this  point  is  that  side-guide 
idlers  are  never  required  on  the  return  run  of  belt  conveyors,  unless  the 
frame  is  out  of  line.  However,  if  the  belt  is  run  over  troughing  idlers  of 
any  kind,  there  comes  a  tendency  to  run  crooked;  this  occurred  with  the 
spool  idlers  used  on  old  grain  conveyors,  and  with  "  dish-pan  "  idlers 
also,  because  if  the  belt  shifted  to  one  side  by  reason  of  eccentric  loading 
or  bad  alignment,  it  acted  as  a  belt  does  in  running  on  to  a  crown-face  pulley, 
that  is,  moved  toward  the  large  part  of  the  pulley. 

The  action  of  a  belt  on  troughing  idlers  is  shown  in  Fig.  79.  Consider- 
ing the  right  half  as  illustrating  a  belt  on  a  spool  idler,  imagine  the  belt 


78 


SUPPORTING  AND  GUIDING  THE  BELT 


\ 


composed  of  strips  1,  2,  3,  4,  5.  If  the  belt  is  very  slack  it  will  take  the 
position  12345  between  idlers,  while  on  the  idlers  it  takes  the  position 
ABCDE.  The  outer  strip  is  deflected  from  5  to  E  and  the  line  of  tension 
along  the  center  of  that  section  is  pulled  out  of  line  for  a  distance  EF, 
where  E  indicates  the  center  of  the  strip  on  the  idler  and  F  is  directly  over  the 
center  of  the  strip  at  5.  The  distance  EF  is  a  measure  of  the  force  parallel 

to  the  face  of  the  pulley,  which 
tends  to  straighten  up  the  pull  in 
the  outer  strip  parallel  to  the 
center  of  the  conveyor;  hence, 
*  section  5,  if  separate,  will  move 
up  on  the  pulley  until  E  coincides 
with  F.  This  force  can  be  called 
T  tang  P,  where  T  is  the  tension 
in  strip  5  and  P  is  the  angle 
between  the  plane  of  the  strip  on 
the  idler  and  its  plane  midway 
FIG.  79.— Steering  Effect  of  Troughing  Idlers,  between  idlers.  That  same  action 

in  the  other  separate  strips  would 

cause  them  to  shift  outward  on  the  pulley  face  for  distances  varying  with 
the  angle  of  inclination  of  the  pulley  at  their  place  of  contact.  If  the 
strips  were  separate,  they  would  run  with  spaces  between  them,  but 
considered  as  parts  of  a  wide  belt,  they  will  tend  to  shift  the-  belt  out  of 
center. 

On  the  left  half  of  Fig.  79,  representing  a  belt  on  a  five-pulley  idler,  the 
action  is  the  same,  although  the  revolving  surfaces  are  those  of  separate 
cylinders  instead  of  parts  of  cones. 

If  the  deflecting  forces  on  one  side  of  the  belt  balance  those  on  the 
other  side,  the  belt  will  run  straight;  if  they  are  unequal,  the  belt  will  shift 
sideways  until  the  balance  is  restored.  Since  the  force  which  moves 
section  F  outward  is  measured  by  tang  P  (Fig.  79)  it  is  evident  that  if  the 
belt  between  idlers  did  not  sag  so  much,  the  tendency  to  run  sideways  would 
be  less,  because  the  angle  P  would  be  less,  and  if  the  belt  did  not  sag  at  all, 
there  would  be  no  tendency  to  run  crooked.  This  fact  explains  why  the  ten- 
dency of  a  belt  to  run  off  to  one  side,  can  sometimes  be  corrected  by  giving 
the  belt  more  tension  on  that  side  by  adjusting  the  take-ups.  The  diagram 
explains  also  why  a  belt  loaded  heavily  on  one  side  tends  to  run  off  on  that 
side.  In  that  case,  the  belt  sags  more  between  idlers  and  the  angle  P  is 
greater,  hence  the  force  outward  parallel  to  the  pulley  face  is  greater.  We 
can  understand  also  why  belts  on  45°  troughing  idlers  are  more  apt  to  run 
crooked  than  on  30°  idlers;  with  all  other  conditions  the  same,  the  natural 
elasticity  of  the  belt  will  cause  it  to  flatten  out  more  between  idlers  and  the 
angle  P  will  be  greater  the  larger  the  angle  of  troughing.  This  elasticity 
is  more  pronounced  in  narrow  belts  than  in  wide  belts.  This  explains  why 
it  is  harder  to  keep  narrow  belts  straight  on  any  kind  of  troughing  idler. 
If  a  pulley  on  one  side  of  an  idler  does  not  revolve  as  freely  as  a  pulley 


STEERING  EFFECT  OF  IDLERS 


79 


on  the  opposite  side  of  the  center  line,  the  deflecting  forces  do  not  balance, 
and  the  belt  runs  crooked.  ^ 

The  sag  of  belt  between  idlers  depends  also  upon  idler  spacing  and  the 
weight  of  the  load.  In  handling  heavy  material,  the  belt  sags  more,  and  the 
angle  P  becomes  greater.  Hence  to  keep  the  belt  straight,  the  troughing 
idlers  must  be  closer  together.  There  are,  of  course,  other  reasons  for  close 
spacing  for  heavy  materials. 

Steering  Effect  of  Idlers. — The  tendency  of  inclined  pulleys  to  steer  a 
belt  or  deflect  its  course,  depends  upon  the  angle  of  inclination  and  the 
proportion  of  belt  width  in  contact  with  them.  It  is  resisted  by  the  propor- 
tion of  belt  width  in  contact  with  the  horizontal  pulley;  hence  we  can 
compare  various  styles  of  idlers  as  to  their  steering  effect  by  multiplying 
each  pulley  face  by  the  tangent  of  the  angle  it  makes  with  the  horizontal, 
and  dividing  their  sum  by  the  width  of  the  belt.  Fig.  80  prepared  on  this 
basis  shows  that  there  is  little  difference  between  the  ordinary  five-pulley 


Angle 

A 


.242 


.182 


FIG.  £0. — Ccmparative  Steering  Effect  of  Different  Troughing  Idlers. 

idler,  column  1,  and  a  three-pulley  idler  troughed  25°  or  30°,  column  3, 
but  that  when  the  horizontal  pulley  has  twice  the  face  of  the  inclined 
pulley,  column  4,  troughing  at  30°  on  three  pulleys  has  less  steering  effect 
than  the  standard  five-pulley  idler  with  angles  15°  and  30°,  column  1. 

Fig.  80  also  shows  that  the  steering  effect  of  a  20°  idler  with  a  broad 
center  pulley,  column  4,  is  about  half  of  that  of  a  standard  five-pulley  idler, 
column  1.  We  should  therefore  expect  the  belt  to  run  straighter  on  the 
former  than  on  the  latter.  If  the  angle  is  reduced  to  10°,  or  even  less  as  in 
flared  idlers,  the  tendency  to  steer  the  belt  is  very  small  as  compared  with 
five-pulley  idlers. 

Methods  of  Making  Belts  Run  Straight. — The  old  original  device  to 
keep  belts  in  place  is  the  side-guide  idler  bearing  against  the  edge  of  the  belt. 
.With  45°  troughing,  they  were  indispensable;  on  five-pulley  idlers  and  30° 
three-pulley  idlers  narrow  belts  still  need  them,  but  on  wider  belts  where  the 
proportion  of  belt  width  acted  upon  by  inclined  pulleys  is  less,  they  are  not 
so  necessary  unless  operating  conditions  are  bad  and  unless  the  methods 
described  below  are  not  effective  in  keeping  the  belt  straight. 


80  SUPPORTING  AND  GUIDING  THE  BELT 

The  effect  of  side-guide  idlers  is  generally  bad.  They  wear  the  belt  at 
its  most  vulnerable  place  and  open  the  way  for  dirt  and  wet  to  get  between 
the  plies  of  fabric.  If  the  belt  is  badly  out  of  line,  the  pressure  against  the 
idler  may  be  enough  to  bend  or  fold  the  belt  for  an  inch  or  two  all  along  the 
edge  so  that  a  crack  develops  there  and  splits  the  belt. 

Another  expedient  to  keep  belts  straight  is  to  set  the  inclined  pulleys 
of  the  troughing  idler  with  a  rake  forward  in  the  direction  of  belt  travel. 
In  the  Mason  patent  of  1907  this  is  done,  as  shown  in  Fig.  81;  another  way 
with  standard  three-pulley  or  five-pulley  idlers  is  to  bevel  the  board  which 
carries  the  idler  so  as  to  tilt  it  forward  (Fig.  82).  In  either  way,  the  effect 
is  to  make  the  inclined  pulleys  rub  the  belt  at  an  angle  to  the  travel  and 
toward  its  center  line.  When  the  belt  is  centered  over  the  idler  these 
forces  balance  by  equality  of  belt  contact  on  the  pulleys;  but  if  the  belt 
runs  off  to  one  side,  the  skewed  pulleys  on  that  side  act  on  more  belt  surface 
and  tend  to  push  it  back  again.  This  method  will  keep  a  belt  straight  where 
other  methods  fail,  but  it  is  hardly  necessary  to  say  that  a  pulley  skewed 
with  reference  to  the  line  of  belt  travel  does  not  revolve  as  freely  as  a  pulley 


FIG.  81. — Guiding  a  Belt  by  Skew-        FIG.  82. — Guiding  a  Belt  by  Tilting 
ing  the  Inclined  Pulleys.  the  Idler  Stands  and  Pulleys. 

set  square  with  the  travel ;  there  must  be  some  waste  of  power  and  some  wear 
on  the  pulley  side  of  the  belt,  and  on  the  rims  of  the  pulleys. 

Before  it  became  customary  to  bevel  the  boards  on  which  five-pulley 
idlers  were  mounted,  it  was  not  uncommon  to  have  serious  trouble  in  getting 
belts  to  run  straight.  An  account  of  twenty-two  belt  conveyors,  nearly  all 
20  inches  wide,  installed  with  five-pulley  idlers  at  a  Western  smelter  in 
1914  says:  "  The  belts  in  the  conveying  system  could  not  be  made  to  run 
true  on  the  troughing  idlers.  To  overcome  their  riding  out  of  position, 
long  boards  were  fixed  at  the  sides  of  the  belt  to  guide  them  and  keep 
them  in  place."  (Bulletin  91  A.  I.  M.  E.)  What  this  did  to  the  edges  of 
the  belts  is  not  stated. 

In  a  few  makes  of  three-pulley  or  five-pulley  idlers  provision  is  made  to 
permit  the  outer  pulleys  to  be  set  slightly  out  of  alignment  with  the  hori- 
zontal pulley,  so  that  by  the  angular  deflection  of  the  pulley,  the  belt  can 
be  steered.  (See  Fig.  71.) 

The  Sibley  patent  of  1916  discloses  an  attempt  to  steer  the  belt  auto- 
matically. The  outer  pulleys  of  a  three-pulley  idler  are  mounted  on  ver- 
tical pivots  which  are  connected  by  cranks  and  a  lever.  If  the  belt  is 
centered  with  reference  to  the  pivots,  the  pulleys  stand  parallel  with  each 


"TRAINING"  A  BELT  81 

Other  and  square  with  the  belt,  but  if  the  belt  runs  higher  up  on  one  pulley, 
its  frictional  contact  there_increase$  and  the  pulley  is  swung  into  an  angular 
position  which  steers  the  belt  back  to  center  again.  This  device  has  not 
had  commercial  use;  dirt,  wet,  and  defective  lubrication  are  some  of  the 
conditions  which  would  interfere  with  its  operation. 

A  number  of  other  schemes  have  been  suggested  to  steer  a  belt  auto- 
matically; they  need  not  be  described,  but  they  are  mentioned  to  show  the 
efforts  made  to  overcome  a  trouble  inherent  in  troughing  idlers. 

"  Training  "  a  Belt. — The  stands  for  troughing  idlers  are  generally  pro- 
vided with  slotted  holes  in  the  base  so  that  the  axis  of  the  pulleys  can  be 
adjusted  square  with  the  center  line  of  the  belt.  When  a  belt  persists  in 
running  crooked,  it  is  usual  to  set  the  stands  out  of  square  with  the  belt 
so  as  to  force  it  in  place  by  a  rubbing  action  similar  to  that  described  above; 
although  in  this  case  the  horizontal  pulley  of  the  idler  also  helps  to  steer 
the  belt.  The  process  of  "  training  "  a  belt  by  adjusting  the  idlers  is,  in 
effect,  setting  the  idler  groups  out  of  square  one  way  or  the  other  enough 
to  counteract  the  tendency  of  the  inclined  pulleys  to  pull  the  belt  crooked. 
Besides  idler  groups  set  out  of  square,  skewed  troughing  pulleys,  and  side- 
guide  idlers,  all  expedients  to  make  a  belt  run  straight  over  troughing  idlers, 
there  is  another  which  may  do  even  more  mischief  because  its  effects  are 
not  immediately  visible.  That  is  the  practice  of  making  it  run  straight 
by  putting  a  high  tension  in  it.  It  is  an  easy  matter  for  the  man  in  charge 
of  a  belt  conveyor  to  correct  faults  inherent  in  the  idlers  or  due  to  poor  align- 
ment by  screwing  the  take-ups  back  (Fig.  113)  or  loading  the  suspended 
pulley  (Fig.  112)  until  the  belt  at  least  stays  on  the  idlers.  That  may  mean 
greater  friction  losses  in  the  machinery,  excessive  stretch  in  the  belt,  splices 
pulling  apart,  frequent  resplicing  and  a  short  life  for  the  belt.  All  of  these 
items  involve  delay,  trouble  and  expense. 

In  general,  the  right  way  to  make  belts  run  straight  is  to  use  flatter 
troughing.  Just  as  30°  troughing  is  better  than  45°  troughing,  so  is  20° 
better  than  30°  in  keeping  the  belt  centered  on  the  idlers  and  running 
straight.  There  is  also  the  collateral  advantage  of  less  longitudinal  bend 
in  the  belt  and  less  tendency  to  crease  or  crack  it.  (See  p.  15.)  The 
maximum  carrying  capacity  for  shallow  troughing  is  less  than  for  30° 
troughing,  but  the  difference  as  stated  in  terms  of  safe  loading  is  not  great. 
(See  Chapter  VII.) 

Internal  Stresses  in  Belts  due  to  Troughing. — All  belts  suffer  internal 
stresses  that  tend  to  shorten  their  lives  when  run  over  troughing  idlers, 
either  from  the  longitudinal  bending  to  the  contour  of  the  idler  or  in  the 
repeated  change  from  the  flat  position  on  the  end  pulleys  to  or  from  the 
troughed  position  on  the  idlers.  When  the  troughing  angle  is  steep,  rubber 
belts  will  stand  the  bending  better  than  stitched  canvas  belts,  but  since  the 
ordinary  safe  carrying  capacity  of  a  belt  is  not  increased  much  by  troughing 
it  beyond  20°  (see  Figs.  133  and  135)  it  is  to  the  owner's  interest  not  to 
use  steep  troughing  with  a  canvas  belt,  nor  in  fact  with  any  kind  of  belt. 
In  most  conveyor  installations  the  price  of  the  belt  is  a  large  percentage  of 


82  SUPPORTING  AND  GUIDING  THE  BELT 

the  total  first  cost  of  the  conveyor,  and  if  the  costs  of  renewals  are  kept 
for  ten,  fifteen,  or  twenty  years  it  will  be  found  that  the  charges  against 
the  belt  for  renewals  and  repairs  will  be  much  greater  than  the  sum  of  the 
charges  against  pulleys,  idlers,  transmission  machinery  and  all  the  rest  of 
the  conveyor  apparatus.  It  pays,  therefore,  with  belts  of  all  kinds,  to  use 
large  pulleys,  well-made  idlers  and  an  angle  of  troughing  as  flat  as  will 
carry  an  economical  load;  for  there  is  no  doubt  that,  other  things  being  equal, 
shallow  troughing  gives  a  longer  life  to  belts  than  steep  troughing,  and  that 
belts  run  flat  and  properly  supported  last  longer  than  belts  troughed  at 
any  angle.  If  shallow  troughing  or  none  at  all  means  a  wider  belt  (see 
p.  86)  the  extra  first  cost  may  be  often  saved  in  lower  charges  for  belt 
renewals  and  repairs. 

Troughing  Canvas  Belts. — The  act  of  troughing  puts  a  tension  on  the 
filler  (crosswise)  threads,  and  since  these  are  more  likely  to  be  cut  and 
worn  by  sharp  pieces  than  the  warp  (lengthwise)  threads  and  since  a  thread 
under  tension  is  more  subject  to  that  kind  of  injury  than  a  slack  thread, 
it  is  evident  that  a  canvas  belt  run  flat  will  be  hurt  less  by  cutting  and 
abrasion  than  a  troughed  belt.  When  a  canvas  belt  is  troughed,  it  is 
better  to  keep  the  inclined  pulleys  rather  far  apart  so  that  the  places  of 
greatest  tension  in  the  filler  threads,  where  the  belt  bends,  will  be  toward 
the  edges  of  the  belt  and  not  near  the  center  where  the  abrasion  under 
the  loading  chute  is  greatest. 

An  idler  designed  especially  for  canvas  belts  is  shown  in  Fig.  67.  It 
has  a  wide  horizontal  pulley  and  the  line  on  which  the  filler  threads  are 
flexed  is  about  halfway  in  from  the  edge  toward  the  middle  of  the  belt. 

Comparison  of  Troughing  Effect,  Three-pulley  or  Five-pulley  Idlers. — 
In  one  respect  a  three-pulley  idler  with  inclined  pulleys  set  at  15°  stresses 
the  belt  less  than  a  standard  five-pulley  idler  which  bends  the  belt  15° 
at  two  places  on  each  side  of  the  middle.  In  the  former,  the  stretch  of  the 
filler  threads  is  spread  over  a  length  equal  to  one-half  the  width  of  the  belt, 
but  on  a  five-pulley  idler  the  stretch  at  A  (Fig.  133)  is  confined  to  the  dis- 
tance BC  and  the  stretch  at  D  comes  on  the  length  of  thread  CE.  Both 
BC  and  CE  are  less  than  one-half  the  width  of  the  belt;  hence  for  equal 
elongation  of  the  lower  plies  at  the  point  of  bend  the  tension  in  the  filler 
threads  may  be  greater  on  the  five-pulley  idler  and  the  tendency  to  crack 
greater.  In  other  words,  the  greater  the  length  of  the  stressed  portion, 
the  less  is  the  stress  for  a  given  deformation.  Reasoning  from  this,  the 
tendency  to  crack  the  belt  on  a  three-pulley  idler  is  least  when  the  face 
of  the  horizontal  pulley  is  about  twice  the  face  of  each  inclined  pulley. 

Canvas  Belts  on  Idlers  Designed  for  Rubber  Belts. — Well-made  stitched 
canvas  belts  saturated  with  Class  1  compounds  (see  p.  47)  and  used 
for  handling  bulk  materials  will  run  on  five-pulley  idlers  or  30°  three- 
pulley  idlers  when  the  belt  is  30  inches  or  wider,  and  the  plies  not  over  6; 
belts  between  18  and  24  inches  in  4-  or  6-ply  will  not  run  well  on  standard 
idlers.  They  should  not  be  troughed  over  20°  and  6-ply  belts  narrower 
than  18  inches  should  not  be  troughed  over  15°;  they  will  not  lie  down  on 


SPOOL  OR  FLARED  IDLERS 


83 


standard  idlers,  but  will  run  crooked  unless  held  in  place  by  side-guide 
idlers,  and  these  are  apt  to  ruin,  the  edge  of  the  belt. 

Spool  or  Flared  Idlers. — The  ol^-time  spool  idler  with  its  deep  concavity 
had  certain  defects  (see  p:  11)  and  has  passed  out  of  existence,  but  a  modi- 
fied form  of  it  is  still  in  use.  In  the  cement  region  of  Pennsylvania  and 
New  Jersey  it  has  survived  the  competition  of  three-pulley  and  five-pulley 
idlers.  As  made  there  by  local  shops  and  by  several  cement  companies, 
it  has  a  cast-iron  center  pulley  with  two  cast-iron  bell-shaped  ends  which 
lift  the  edge  of  the  belt  an  inch  or  two.  (Fig.  83.)  The  middle  section  and 
the  two  end  sections  are  tight  on  the  shaft,  consequently  there  is  always 
some  wear  on  the  pulley  side  of  the  belt  near  its  edges  and  on  the  bell- 
shaped  ends,  but  this  wear  is  often  less  than  might  be  supposed.  In  most 
cases  the  life  of  the  belt  is  determined  by  the  more  serious  wear  on  the 


FIG.  83. — 24-inch  Belt  on  Cast-iron  Spool  Idlers  Carrying  Cement  Clinker. 

upper  surface.  A  24-inch  belt,  700-feet  centers,  horizontal,  installed  in 
1908  is  still  in  use  (1922)  carrying  crushed  coal  with  the  original  flared  idlers 
still  in  place. 

Belts  carried  by  flared  idlers  are  nearly  flat,  the  slight  lift  of  the  edges 
serving  to  prevent  loss  of  material  in  transit,  but  not  permitting  the  belt 
to  convey  so  much  as  a  belt  run  over  multiple-pulley  idlers.  On  the  other 
hand,  the  belts  run  straight  without  dependence  on  skewed  pulleys  or  side- 
guide  idlers.  Still  more  important,  the  lubrication  is  simple,  it  is  confined  to 
babbitted  bearings  in  which  the  shaft  turns  and  it  is  more  certain  than 
the  greasing  of  a  number  of  loose  pulleys  through  one,  two  or  three  hollow 
shafts  each  with  its  side  outlet  holes. 

Flared  idlers  used  in  damp  and  dirty  places  may  accumulate  crusts  of 
material  which  may  injure  the  belt.  For  this  reason,  and  because  the 
carrying  capacity  is  less,  they  are  not  so  general  in  their  application  as  three- 


84 


SUPPORTING  AND  GUIDING  THE  BELT 


r 


FIG.  84.— Uniroll  Flared  Idler  with  Oil  Lubrication 
(Link-Belt  Company.) 


pulley  and  five-pulley  idlers.  In  any  case,  the  obvious  advantages  of  the 
flared  idler  in  simplicity  of  construction  must  be  weighed  against  its  equally 
obvious  limitations. 

The  Uniroll  idler  of  the  Link-Belt  Company  is  a  commercial  develop- 
f  ment  of  the  flared  idler  de- 

scribed above.  It  consists 
of  a  steel  tube  fastened  to 
malleable-iron  bell-shaped 
ends  and  mounted  on  a 
straight  shaft  supported  in 
trunnion  bearings.  The 
bearings  are  made  with  oil- 
wells  for  chain-oiling  (Fig. 
84)  or  with  roller  bearings 
or  with  screw  cups  for 
grease  lubrication.  Figure 
85  shows  the  assembly  of 
a  carrying  idler  and  of  a 
return  idler.  Tables  13  and 
14  give  the  principal  dimen- 
sions. 

For  carrying  capacities  of  belts  on  Uniroll  idlers,  see  p.  146. 
Troubles  with  Multiple  Pulley  Idlers  have  led  some  concerns  to  discard 
them  and  substitute  plain  flat  pulleys  with  no  troughing.     Figure  86  shows  a 
24-inch  6-ply  belt  carrying  50  tons  of  crushed  limestone  per  hour  on  flat 
idlers  at  225  feet  per  minute. 

The  vice-president  and  super-  U-     F.or  £ete°"1? g  Be.Vlngl- 

intendent  of  the  company 
operating  it  says:  "  My  per- 
sonal opinion  based  on  ex- 
perience with  conveyor  belts 
is  that  no  type  of  troughing 
idler  is  desirable  because 
lubrication  is,  as  a  rule,  not 
properly  attended  to  and  the 
pulleys  are  allowed  to  stick, 
wear  flat  and  then  cut  the 
belt.  Troughing  idlers  all 
have  the  tendency  to  break  a 
belt,  due  to  the  constant 
bending  between  the  flat  head 
and  tail  pulleys  and  the 
troughing  idlers.  At  our  plant  here  I  have  adopted  the  flat  belt  and 
figure  it  wide  enough  to  have  a  clear  space  of  6  inches  on  each  side  of  the 
material.  With  such  a  width  it  hardly  ever  happens  that  any  stones  or 
other  material  will  roll  off."  "  The  trouble  with  belt  conveyors,  as  a  rule, 


FIG.  85. — Dimensions  of  Uniroll  Idlers  and  Return 
Idlers. 


TROUBLES.  WITH  MULTIPLE  PULLEY  IDLERS 


85 


TABLE  13.— DIMENSIONS  OF  UNIROLL  IDLERS 

(link-Belt  Company) 

CARRYING  IDLERS 


Width  of  Belt,  Inches 

12 

14 

16 

18 

20 

24 

30 

36 

42 

48 

54 

A 
B 
C 
E 
R 
F 
H 
L2 
U 
V 
W 
M 
N 

4" 

4|" 
7f 

1'  3" 

6" 
1'    8f 
1'   8f" 

47 
63 

1'   2f 

4" 
6f 
6f 

1'  X5" 
6" 
1'  10f" 

r  lof  " 
"so" 

67 

1'   4f 

4" 
6f 

1'  "" 

1'    Gf 

51" 
7|" 
6f" 

M" 
1'   9" 

1'    8f 
5f 

si" 

1'   3|" 

IA;; 

2'   Of 

51" 

r  of" 
iA" 

2'   3" 

2'    6f 

i'  ef" 

1'   3f" 
2'  *9" 

3'    Of 
51" 

7f" 
2'    Of" 

r  sf" 

3'  X3" 

3'    6f 
6f" 
9f 
2'    3f" 

3'  10" 

4'    0^" 
6f" 
9^" 
2'    9f" 
1'    Sf 

iA" 

4'    4" 

4'   6^" 
6f" 
9i" 
3'   3|" 

4'  10" 

6" 
2'   Of" 
2'   Of" 

52 

70 

6" 
2'   21" 
2'   4f 
2'   Sf 
62 
82 

6" 
2'   41" 
2'    6£" 
2'    7f 
65 
86 

6" 
2'   81" 
2'  lOf 
2'  llf 
71 
95 

6" 
3'    21" 
3'    4f 
3'   Sf 

82 
109 

6" 
3'    81" 
3'  lOf 
3'  llf 

87 
118 
10" 

7" 
4'    31" 

4'    7f 
12" 

7" 
4'    91" 

5'    If 
12" 

7" 
5'   3f" 

12" 

7" 

7" 

8" 

8" 

8" 

8" 

10" 

Plank  bases  for  stands  if  X5f"  up  to  42",  If  X7f"  for  42"  and  over. 
Channel  bases  for  stands  6",  8  Ib.  up  to  42",  8",  llj  Ib.  for  42"  and  over. 
NOTE. — U  is  for  chain  oiling,  V  is  for  grease-cup,  W  is  for  Hyatt  roller  bearings. 

M  is  weight  (Ibs.)  of  complete  idler  including  plank  base. 

N  is  weight  (Ibs.)  of  complete  idler  including  channel  base. 

TABLE  14.— DIMENSIONS  OF  UNIROLL  IDLERS 

(Link-Belt  Company) 

RETURN  IDLERS 


Width  of  Belt,  Inches 


12 

14 

16 

18 

20 

24 

30 

36 

42 

48 

54 

J 

4" 

4" 

4" 

5i" 

51" 

51" 

51" 

51" 

51" 

51" 

51" 

K 

I'    1" 

1'   3" 

1'   5" 

r  7" 

1'  10" 

2r    2" 

2'   8" 

3'    2" 

3'    8" 

4'    2" 

4'  8" 

F 

ft" 

W 

H" 

i&" 

iiV' 

1&" 

IiV' 

i  A" 

liV' 

liV' 

iA" 

X 

2'    5|" 

2'    7|" 

2'    9*" 

2'  llf" 

3'    If' 

3'    5f" 

3'  llf" 

4'   5f  ' 

4'  llf 

5'    5f 

5'  llf 

Y 

2'    5f" 

2'    7f" 

2'   9f" 

3'    H" 

3'  sr 

3'  7r 

4'    U" 

4'   7*" 

Z 

3'    2£" 

3'  4r 

3'   84" 

4'  2r 

4'  sr 

5'   3-^" 

5'    9^" 

6'   3|" 

G, 

1'    8" 

1'   8" 

1'   9" 

1'   9" 

1'   9" 

1'   9" 

1'llt" 

I'n*" 

2'    If" 

2'    If 

2'    If 

S 

44 

47 

49 

64 

68 

73 

82 

90 

NOTE. — X  is  for  chain  oiling,  Y  is  for  grease-cup,  Z  is  for  Hyatt  roller  bearings. 
S  is  weight  (Ibs.)  of  complete  return  idler. 

is  not  so  much  the  conveyor  itself,  but  the  ignorance  of  the  labor  which 
looks  after  such  machinery  around  plants  like  ours.  This  labor  is  shift- 
less, careless  and  does  not  pay  proper  attention  to  machinery  in  watching 
and  lubricating  it.  I  would  frankly  say  that  few  belts  are  worn  out; 
most  of  them  have  to  be  replaced  because  of  abuse." 


86 


SUPPORTING  AND  GUIDING  THE  BELT 


For  carrying  capacity  of  flat  belts,  see  p.  146. 

Deep  Troughing  or  No  Troughing. — In  1908  when  the  five-pulley  idler 
was  just  coming  into  use  and  when  most  of  the  three-pulley  idlers  in  use 
had  angles  of  30°  or  35°  an  engineer  prominent  in  the  belt  conveyor  business 
said  (Transactions  A.  S.  M.  E.,  Vol.  30):'  "  The  only  object  of  troughing 
is  to  get  an  increase  of  capacity  so  that  when  a  belt  has  to  be  renewed  it 
will  cost  less  money.  Unless  we  get  a  substantial  increase  of  capacity  by 
a  good  deep  trough,  what  is  the  use  of  troughing  at  all,  thereby  sacrificing 
the  simplicity  of  the  single  roller  that  suffices  to  carry  the  flat  belt."  This 
argument  states  the  case  correctly  so  far  as  the  width  of  the  belt  is  con- 
cerned, because  the  safe  carrying  capacity  of  a  belt  on  three-pulley  or  five- 
pulley  idlers  is  double  that  of  a  flat  belt  (see  p.  146)  and  50  or  60  per  cent 


FIG.  86.— 24-inch  Flat  Belt  Carrying  Crushed  Stone. 

more  than  when  the  belt  is  run  over  ordinary  flared  idlers  and,  consequently, 
for  a  given  capacity,  a  conveyor  with  a  narrow  troughed  belt  will  cost  less 
than  one  with*  a  wider  flat  belt.  On  the  other  hand;  the  flat  belt  will  run 
straight,  will  not  need  side-guide  idlers  and  will  not  crack  lengthwise  from 
troughing.  The  greater  width  may  permit  the  use  of  a  wider  and  better 
loading  chute  and  a  better  distribution  of  the  wear  over  the  belt  surface, 
and  altogether  the  wider  flat  belt  may  last  enough  longer  than  the  narrower 
troughed  belt  to  justify  the  added  expense.  The  experience  of  the  years 
since  1908  has  shown  that  belt  capacity  is  not  always  the  most  important 
consideration;  simplicity  of  construction  and  certainty  of  lubrication  are, 
in  many  installations,  factors  of  greater  importance. 

Lubrication  of  Idlers. — Quite  early  in  his  experience,  Mr.  Robins  dis- 
carded oil  lubrication  (see  Fig.  34)  because  it  was  difficult  with  his  idler 


GREASE  OR  OIL 


87 


to  prevent  belts  from  being  injured  by  oil  dripping  or  scattering  from  the 
pulleys.  He  found  grease  more  convenient.  The  pulleys  did  not  turn 
quite  so  freely,  but  the  leakage  #£  grease  from  the  pulley  bores  formed  a 
collar  which  prevented  Bust  and  dirt  from  getting  in.  There  was  usually 
no  drip  of  grease  onto  the  belt  and  its  use  was  an  advantage  in  places  like 
stone-crushing  plants,  where  the  air  was  full  of  dust. 

There  were,  however,  some  collateral  disadvantages  which  were  apparent 
to  designers  and  users  of  belt  conveyors  after  some  years  of  experience. 
In  some  large  plants  it  requires  the  full  time  of  several  men  to  keep  grease 
cups  filled  and  the  caps  screwed  down.  It  sometimes  happens  that  the 
first  evidence  of  lack  of  such  care  is  costly  damage  to  the  belt.  If  the 
attendant  misses  a  cup,  no  grease  is  forced  through  the  hollow  shaft,  a  pulley 
refuses  to  turn,  the  belt  slides  over  it,  wears  the  rim  thin  and  finally  cuts 
it  away  with  the  result  that  the  belt  is  cut  on  the  sharp  edges.  This  Is 
more  likely  to  happen  on  the  return  run  where  the  grease  cups  are  low 
and  hard  to  get  at  and  where  the  idlers  are  often  concealed  by  the  supporting 
frame  or  by  the  protective  deck.  In  this  location  a  failure  of  the  pulleys 
to  turn  is  not  so  easily  seen  as  when  that  trouble  occurs  on  the  carrying  run. 

In  some  plants  equipped  with  many  belt  conveyors  the  cost  of  grease 
and  the  labor  of  filling  and  adjusting  the  cups  amounts  to  a  large  sum  in  the 
course  of  a  year.  At  one  plant  that  uses  about  15,000  feet  of  wide  belts, 
grease  costs  over  $2000  a  year  and  the  labor  charge  is  over  $7000  a  year 
(1920).  All  the  belts  in  this  plant  do  not  run  every  day;  if  they  did,  the 
charges  would  be  considerably  more.  In  another  plant  that  uses  about 
8000  feet  of  belt  four  men  are  employed  in  attending  to  grease  cups  on  the 
conveyors. 

Grease  or  Oil. — It  is  well  understood  that  grease  lubrication  is  best  for 
heavy  pressures  and 
low  velocities  and  that 
oil  is  better  suited  to 
lower  pressures  and 
higher  velocities.  This 
is  shown  in  Fig.  87 
based  on  Tower's  ex- 
periments (see  Kent's 
M.  E.  Pocketbook), 
comparing  grease  and 
oil  at  a  temperature  of 
90°  with  flooded  lubri- 
cation. At  pressures  over  500  pounds  per  square  inch  there  is  not  much 
difference  between  grease  and  oil,  whether  the  journal  speed  is  157  feet  or 
471  feet  per  minute,  but  at  lower  pressures  the  difference  is  quite  marked, 
and  below  200  pounds  per  square  inch  the  coefficients  for  grease  increase 
more  rapidly  than  those  for  oil.  At  100  pounds  per  square  inch  the 
coefficients  were  as  2  to  1  within  the  range  of  speeds  tested. 

The  Tower  experiments  were  not  carried  below  100  pounds  per  square 


.001   .002  .003   .004  .006   .006    .007  .008   .009    .010  .011   .012.  J)13  .014  .015 

Coefficients  of  Friction 

FIG.  87. — Comparison  of  Coefficients  of  Friction,  Grease  or 
Oil  Lubrication. 


88  SUPPORTING  AND  GUIDING  THE  BELT 

inch,  but  since  the  Galton-Westinghouse  experiments  (see  Kent's  M.  E. 
Pocketbook)  showed  that  at  velocities  below  100  feet  per  minute  and  at 
low  pressures  the  friction  varied  directly  as  the  pressure,  we  may  say  that 
for  copious  lubrication  at  speeds  under  157  feet  per  minute  and  at  pressures 
below  100  pounds  per  square  inch  oil  offers  one-half  the  resistance  that 
grease  does.  In  commercial  belt  idlers  the  pressure  in  the  bores  of  the 
pulleys  is  much  less  than  100  pounds  per  square  inch  and  the  speed  of  the 
lubricated  surfaces  is  less  than  157  feet  per  minute.  Considering  these 
facts  and  also  that  a  bearing  can  be  "  flooded  "  with  oil  more  easily  and  with 
greater  certainty  than  with  grease,  it  seems  safe  to  say  that  the  coefficient 
of  friction  for  grease  lubrication  as  applied  to  belt  idlers  is  more  than  twice 
the  coefficient  for  oil  lubrication — that  is,  to  turn  greased  idlers  requires 
more  than  twice  as  much  pull  as  to  turn  oiled  idlers. 

Oil  Lubrication  for  Idlers. — Although  the  Robins  type  of  single-plane 
idler  was  particularly  suited  to  grease  lubrication,  there  have  been  several 
designs  of  idlers  of  that  type  with  tight  pulleys  on  shafts  running  in  self- 
oiling  bearings,  but  they  never  reached  the  commercial  stage.  Some  of 
these  are  shown  in  Acklin's  patent  702273,  June  10,  1902,  and  Bee's  patent 
800786,  October  3,  1905.  The  bearings  for  the  horizontal  shaft  are  hard 
to  get  at;  it  is  difficult  to  see  whether  the  bearing  holds  the  right  quantity 
of  oil,  and  in  the  act  of  filling  them  oil  is  apt  to  get  on  the  pulleys  and  on  the 
belt.  In  the  self-oiling  grain  conveyor  idler  made  by  several  manufacturers 
no  attempt  is  made  to  set  the  three  pulleys  in  line;  it  follows  original 
grain  conveyor  practice  in  having  the  pulleys  mounted  in  two  planes. 
The  pulleys  are  all  tight  on  their  shafts;  the  horizontal  shaft  turns  in  ring- 
oiling  bearings  that  carry  a  supply  of  oil  and  in  which  the  oil  level  can  be 
seen.  The  troughing  idler  (Bee  patent  699477,  May  6,  1902)  is  tight  on  a 
stud  which  runs  within  a  bearing  submerged  in  oil  and  which  can  easily 
be  inspected  and  filled.  The  mounting  is  like  that  of  Fig.  27  or  Fig.  28. 

In  flat  idlers  or  idlers  of  the  Uniroll  type  it  is  easy  to  take  advantage  of 
oil  lubrication.  The  through  shaft  which  carries  the  pulleys  runs  in  bab- 
bitted bearings  (Fig.  84)  fitted  with  oil  rings  or  chains  that  dip  down  into 
an  oil  well  in  the  base  of  the  casting.  This  contains  enough  oil  to  last  some 
months;  the  level  of  the  oil  and  the  actual  lubrication  of  the  shaft  can  be 
seen  by  turning  aside  a  spring  cover  on  the  bearing. 

The  pull  required  to  move  a  belt  over  idlers  of  this  type  is  not  over  60 
per  cent  of  that  required  for  five-pulley  idlers  with  grease  lubrication. 

Ball-bearing  Idlers  were  made  in  a  tentative  way  for  years  by 
several  manufacturers;  in  most  of  them  the  cast-iron  pulleys  were  bored  and 
fitted  with  a  self-contained  ball  bearing  at  each  end  of  the  hub.  These 
required  a  higher  grade  of  shop  work  than  is  usually  put  on  belt  idlers. 
They  were  expensive  and  did  not  sell  well. 

Idlers  with  Sheet-steel  Pulleys. — In  1912  J.  L.  Wentz  patented  a  simpler 
three-pulley  idler  in  which  there  were  no  through  shafts.  Each  of  the 
three  sheet-steel  pulleys  (Fig.  88)  had  a  stamped  steel  head  recessed  to 
receive  a  ball  bearing,  the  inner  race  of  which  was  carried  by  a  lug  rigidly 


UNIT  CARRIER  OF  THE  STEPHENS-ADAMSON  CO. 


89 


Not  many  of  these  idlers 


111.)  repre- 


FIG.  88.— Detail  of  3-pulley  Ball  Bearing 
Idler  without  Through-shafts.  (Robins' 
Conveying  Belt  Co.) 


fastened  to  the  supporting  frame  of  the  idler. 

have  been  made. 

The  Unit  Carrier  of,  the   Ste^hens-Adamson  Co.  (Aurora, 

sents  the  development  of  a  ball-bear- 
ing idler  into  commercial  form.     The 

"  single  unit  "  (Fig.  89)  consists  of  a 

stamped  steel   pulley  with   each  end 

recessed    to    receive    a    ball   bearing 

with  hardened  races;  a  pressed  steel 

yoke  forms  a  stand  for  the  pulley ;   a 

slot  at  the  top  edge  fits  the  milled  end 

of  the  pulley  shaft  and  prevents  it  from 

turning.     The  units  can  be  assembled 

into  groups  of  2,  3,  4  or  5  to  form  idlers  of  various  widths  and  different  angles 

of  troughing  (Fig.  90).     The  construction  of  the  pulley  is  shown  in  Fig.  91. 

The  ball  bearing  is  placed  in  a  deep  depression  in  the  end  of  the  pulley  and 
a  felt  packing  ring  R  compressed  between  two 
washers  helps  to  keep  out  dirt  and  prevent  the 
escape  of  lubricant  with  which  the  bearing  is  packed. 
A  square  shaft  holds  the  felt  ring  and  the  washers 
and  also  the  inner  ball-race  from  rotating. 

These  idlers  are  light  and  strong  and  can  be  sold 
at  a  price  to  compete  with  plain  grease-cup  idlers. 
The  bearings  are  filled  with  grease  when  shipped 
and  if  opened  and  repacked  at  regular  intervals  of 
some  weeks  or  months  they  run  well  and  last  long. 

The  manufacturers  advertise  that  these  idlers 
save  25  per  cent,  of  power  in  horizontal  conveyors 
of  ordinary  length,  and  since  they  do  not  require 

attention  frequently,  they  save  also  in  attendance  and  cost  of  lubricant. 

When  it  is  necessary  to  repack  the  bearings  with  grease  it  is  more  convenient 


FIG.  89.— Ball-bearing 
Sheet-steel  Pulley 
with  Sheet-steel 
Stand.  (Stephens- 
Adamson  Mfg.  Co.) 


FIG.  90.— 5-pulley   Troughing    Idler   Built   of   Assembled    Units. 

Mfg.  Co.) 


(Stephens-Adamson 


in  most  cases  to  remove  the  idler  entirely  and  slip  a  spare  set  mounted 
complete  in  place  of  it.  This  is  true  especially  of  wide  belts,  because  it  is 
inconvenient  to  remove  the  pulleys  and  do  the  repacking  under  the  belt. 


90 


SUPPORTING  AND  GUIDING  THE  BELT 


In  long  conveyors  the  saving  of  power  is  more  than  25  per  cent.     A 

coal  conveyor  at  a  mine  in  western  Pennsylvania  has  a  42-inch  belt  running 

at  358  feet  per  minute  on  five-pulley  ball- 
bearing idlers  spaced  3  feet  6  inches  and  rising 
2  feet  in  675-foot  centers.  The  conveyor  is 
driven  by  tandem  pulleys  on  the  return  run 
near  the  foot  and  it  has  a  regular  capacity  of 
540  tons  per  hour.  Repeated  tests  with 
recording  instruments  show  20  h.p.  or  less 
when  the  ball  bearings  are  in  good  condition. 
The  rule  stated  on  page  97  gives  56  h.p. 

Roller-bearing  Idlers. — The  hollow  spiral 
roller  bearing  (Fig.  92)  made  by  the  Hyatt 
Roller  Bearing  Co.,  New  York,  has  been 
applied  to  belt-conveyor  idlers  in  several 
ways.  In  five-pulley  idlers  the  construction 

used  is  that  shown  in  Fig.  93.     Each  pulley  is  bored  to  receive  the  hardened 

steel  sleeve  which  forms  the  outer  shell  of  the 

bearing;   steel  ple.tes  pressed  into  the  bored 

hole  hold  the  roller  bearing  in  place,  and  loose 

steel  washers   filling  the  space  between  the 

pulley  hub  and  the  hub  of  the  stand,  take  the 

end-thrust  due  to  the  inclined  position  of  the 

pulley.     Four  grease  cups  are  used  for  each 

troughing  idler,  so  that  grease  does  not  have 

to  be  forced  through  the  roller  bearing  in  one 

pulley  to  reach  the  next  one. 

For  return  idlers,  horizontal  carrying  idlers  of  grain  conveyors,  and 

Uniroll  or  flared  idlers,  the  construction  is  simpler  (Fig.  94).     The  stands 

carry  trunnion  bearings  closed  at  one  end  and  bored  to  receive  the  shell 


FIG.  91. — Stephens-Adamson 
Ball-bearing  Pulley. 


FIG.  92.— Hyatt  Roller  Bearing. 


FIG.  93. — Roller  Bearings  Applied  to  5-pulley  Troughing  Idler. 


ROLLER-BEARING  IDLERS 


91 


of  the  roller  bearing.     The  pulley  is  tight  on  the  shaft.     Each  idler  then 
takes  two  roller  bearings  instead*  of  five;  lubrication  is  at  two  points  instead 


End  Plate  Press 
Fit  in  Bore 


Oil  Sling 


FIG.  94. — Assembly  of  Flared  Idler 
with  Two  Roller  Bearings. 


FIG.  95.— Oil  Lubricated  Roller  Bearing  for 
Flared  Idler. 


FIG.  96. — Grain  Conveyor  Concentrator 
Pulley  Fitted  with  Roller  Bearings. 


of  four;    none  of  the  grease  cups  are  under  the  belt  and  since  there  is  no 

end-thrust  due  to  inclined  pulleys,  there  is  no  friction  outside  of  the  roller 

bearings  and  no  wear  on  stands  or 

on  pulley  hubs. 

Fig.  95  shows  a  roller  bearing  for 

a  flared  idler  designed  for  oil  lubri- 
cation  and  for   heavy  work.      The 

shaft  is  ITIT  inches,  the   speed    380 

r.p.m.  and  the  load  per  bearing  400 

pounds. 

Fig.    96    shows    a    Hyatt    roller 

bearing   applied    to   a    concentrator 

pulley.      Side-guide    idlers    can    be 

fitted  with  them  in  a  similar  way. 
The  Stearns  idler,  made  by  the 

Stearns   Conveyor    Co.,    Cleveland, 

Ohio,  resembles  the  Stephens-Adamson  unit  carrier  in  being  made  of  3,  5 

or   more   sheet-steel    pulleys  carried  on    independent  shafts  and  mounted 

on  a  bent  .supporting  alible.  The  principal 
feature  of  the  pulley  is  a  central  grease 
chamber  with  a  spring  plunger  (Fig.  97).  The 
fixed  shaft  on  which  the  pulley  turns  is  hollow 
and  has  a  pipe  connection  to  which  a  grease 
gun  can  be  applied.  When  grease  is  forced 
through  the  shaft  the  spring  plunger  is  pressed 
back  and  the  chamber  is  filled.  After  that, 
the  spring  acts  for  a  period  of  some  weeks  or 
months  to  force  grease  into  the  bearings  in 
the  pulley.  Instead  of  the  roller  bearings 

shown  in  Fig.  97,  the  pulley  can  be  fitted  with  ball  bearings  or  Babbitt 

metal  bushings. 


FIG.    97.  —  Stearns   Sheet-steel 
Pulley  with  Grease  Chamber. 


92  SUPPORTING  AND  GUIDING  THE  BELT 

Advantages  of  Ball-bearing  and  Roller-bearing  Idlers. — As  compared 
with  grease-lubricated  idlers,  idlers  with  ball  or  roller  bearings  have  several 
advantages. 

1.  Less  power  to  run  the  conveyor. 

2.  Less  tension  on  the  conveyor  belt. 

3.  Less  expense  for  attendance  and  for  lubricant. 

4.  Less  chance  that  the  idlers  will  stick  tight  or  drag  and  injure  the  belt. 
The  saving  of  power  cannot  be  estimated  by  a  comparison  of  the  coef- 

ficents  of  friction  for  the  two  kinds  of  bearing.  The  reason  is  that  the 
horse-power  formulas  in  use  for  grease-lubricated  bearings  are  based  on  an 
empirical  coefficient  of  friction  (see  p.  96)  which  includes  not  only  the 
friction  in  the  idler  bearings,  but  also  the  bending  of  the  belt,  getting  the 
material  up  to  speed  at  the  loading  point,  the  slight  lifting  and  squeezing 
of  the  load  in  passing  over  the  idlers,  the  friction  of  foot  shafts,  snub  shafts, 
etc.  It  is  not  possible  in  theory  nor  in  practice  to  separate  the  horse- 
power required  for  these  various  items,  hence,  while  we  may  say  that  /,  the 
coefficient  for  journal  friction  in  a  greased  bearing,  is  .07  and  that  a  roller 
bearing  will  show  as  low  as  .0025,  it  does  not  follow  that  the  power  con- 
sumed is  in  the  ratio  of  those  figures  or  as  1  to  28. 

Tests  of  a  24-inch  belt  conveyor,  50-foot  centers  inclined  at  15°  and 
heavily  loaded  to  require  10  h.p.  showed  less  than  1  h.p.  saving  when  its 
idlers  were  fitted  with  roller  bearings.  In  these  tests  about  half  the  power 
was  consumed  in  motor  losses,  losses  in  power  transmission,  friction  of  head 
shaft,  two  countershafts  and  foot  shaft.  In  addition,  2  h.p.  was  required 
to  lift  the  load;  this  is  independent  of  the  nature  of  the  idlers,  so  that  the 
saving  of  power  in  these  tests  due  to  the  use  of  roller-bearing  idlers  was  less 
than  30  per  cent.  The  saving  in  power,  is  of  course,  more  marked  in  long 
conveyors  where  a  greater  part  of  the  power  is  used  up  in  overcoming  idler 
friction.  The  following  case  illustrates  this:  A  44-inch  belt  conveyor 
605-foot  centers,  rising  76  feet,  carried  stone  at  1220  tons  per  hour.  Trough- 
ing  idlers  were  like  Fig.  93;  return  idlers  also  had  roller  bearings.  Tests 
with  recording  instruments  showed  134  h.p.  The  manufacturer's  calculated 
rating  for  this  conveyor  working  with  grease-cup  idlers  was  198  h.p.,  of 
which  94  h.p.  was  for  lifting  the  load  through  76-foot  vertical  height  and 
is  therefore  to  be  deducted  for  any  comparison  of  the  qualities  of  the  idlers. 
The  saving  of  power  attributed  to  the  use  of  Hyatt  roller  bearings  was  in 
this  case  104-40  =64  h.p.,  or  60  per  cent  of  the  power  due  to  the  friction 
load,  or  considering  the  motor  horse-power,  the  saving  was  y694¥  or  over 
30  per  cent. 

The  following  records  of  recent  tests  of  conveyors  fitted  with  roller 
bearings  in  five-pulley  idlers  will  be  of  interest. 

1.  48-inch  belt,  387-foot  centers,  sloped  18°,  lift  109  feet,  carrying  795 
tons  run-of-mine  coal  per  hour  at  483  feet  per  minute;  150  h.p.  motor  used. 

Readings  with  electrical  instruments  showed  107  h.p. 

Formula  2  (p.  97)  for  grease  lubrication  gives  137  h.p. 

Formula  4  (p.  98)  for  grease  lubrication  gives  148  h.p. 


SAVING  IN  BELT  DUE  TO  IMPROVED  IDLERS  93 

2.  48-inch  belt,  405-foot  centers,  sloped   19°,  lift   119  feet,   carrying 
1030  tons  run-of-mine  coal  per  hou'r  at  506  feet  per  minute;   150  h.  p.  motor 
used.  4» 

Readings  with  electrical  instruments  showed  162  h.p. 
Formula  2  (p.  97)  for  grease  lubrication  gives  190  h.p. 
Formula  4  (p.  98)  for  grease  lubrication  gives  206  h.p. 

3.  42-inch  belt,  600-foot  centers,  sloped  18°,  lift  114  feet,  carrying  324 
tons  run-of-mine  coal  per  hour  at  242  feet  per  minute;   100  h.p.  motor 
used. 

Readings  with  electrical  instruments  showed  52  h.p. 

Formula  2  (p.  97)  for  grease  lubrication  gives  71  h.p. 

Formula  4  (p.  98)  for  grease  lubrication  gives  76  h.p. 

In  another  case  cited  by  the  makers  of  these  bearings,  the  reduction  in 
the  power  required  made  a  saving  of  $1000  in  the  price  of  the  motor,  and 
since  a  belt  of  lighter  ply  could  safely  be  used,  a  reduction  of  $2700  was 
made  in  that  item. 

Saving  in  Belt  Due  to  Improved  Idlers.  —  The  reduction  in  the  thick- 
ness of  the  belt  referred  to  above  may  be  illustrated  by  an  example.  (For 
explanations  of  these  calculations  see  pp.  109,  110.)  A  certain  30-inch 
6-ply  belt  running  at  300  feet  per  minute  took  30  h.p.  The  horse-power 

30  X33  000 

pull  or  Ti—  Tz  was  therefore  -  -  --  =3000  pounds.     The  head  pulley 

300 

was  lagged  and  with  a  snub  pulley  there  was  a  belt  wrap  of  240°.  From 
Table  21,  Ti  was  then  3300x1.30  =  4290-pound  pull  on  the  loaded  belt. 

4290 

From  Table  20,   the  slack  tension   T2  was—  -  =990  pounds.     The  unit 

4.33 

tension  in  the  belt  was  -  -  —  =24  pounds  per  inch  per  ply. 
30X6 

If  by  the  use  of  ball-  or  roller-bearing  idlers  the  power  could  be  reduced 
to  25  h.p.,  then  the  horse-power  pull  is  2750  pounds,  7^=3575  pounds 
and  T2  =825  pounds;  and  a  5-ply  belt  could  be  used  without  increasing  the 

3575 

unit  tension  in  the  fabric  because  -  =24  pounds  per  inch  per  ply.     But 

ou  X  o 

if  for  other  reasons  it  were  desirable  to  use  a  6-ply  belt,  then  it  would  be 
possible  to  use  its  available  strength  to  dispense  with  the  snub  pulley  and 
use  a  belt  wrap  of  180°.  For  that  condition  Ti  =2750  X  1.50  =4125  pounds 


(Table  21)  and  T2  =-  =1375  pounds  (Table  20).     That  is,  by  increas- 

o 

ing  the  slack  tension  by  385  pounds  the  6-ply  belt  will  pull  the  load  without 
the  use  of  a  snub  pulley  and  there  will  be  no  reverse  bend  in  the  belt. 

Saving  in  Repairs  and  Replacements.  —  The  freedom  with  which  ball- 
bearing or  roller-bearing  idlers  turn  means  more  than  a  saving  of  power; 
it  means  that  there  will  be  less  rubbing  on  the  rims  of  the  pulleys,  fewer 
replacements  of  pulleys  and  less  chance  of  cutting  and  scraping  the  belt 
over  pulley  rims  that  have  been  worn  thin  and  cut  through.  Replace- 


94  SUPPORTING  AND  GUIDING  THE  BELT 

ment  of  idlers  is  not  a  serious  matter  in  most  plants,  but  in  others,  even 
where  gritty  material  is  not  handled,  grease-cup  idlers  wear  out  regularly. 
In  one  plant  that  uses  about  8000  feet  of  belt  for  conveying  run-of-mine 
and  crushed  coal,  the  replacements  of  idlers  for  worn-out  and  broken 
pulleys  and  stands  per  year  for  a  number  of  years  averaged  over  15  per 
cent  of  the  number  in  use. 

Saving  in  Labor  and  Attendance. — They  save  also  in  attendance  and 
cost  less  for  grease.  It  is  estimated  that  for  one  year  of  ordinary  service 
the  following  quantities  of  grease  are  required  for  each  cup  of  grease- 
lubricated  idlers:  No.  2  cup,  6  pounds;  No.  3  cup,  12  pounds;  No.  4  cup, 
20  pounds.  The  time  needed  to  fill  each  cup,  over  and  above  the  ordinary 
screwing  down,  will  average  about  two  hours  per  year  per  cup. 

On  the  cost  of  grease  and  the  filling  of  grease  cups  see  also  p.  87. 

When  roller  bearings  are  fitted  to  five-pulley  idlers  (Fig.  93)  there  is  a 
saving  in  power  which  in  large  conveyors  becomes  very  important  (see 
instances  above).  There  is  also  a  saving  in  attendance  and  in  the  amount 
of  lubricant  required,  because  the  bearings  need  only  a  small  quantity  of 
grease  and  the  cups  need  not  be  screwed  up  often.  In  this  respect  alone 
roller-bearing  idlers  bring  a  good  return  on  the  investment  over  and  above 
the  saving  in  power.  In  plants  with  only  one  or  two  belt  conveyors  the 
machine  is  looked  after  with  care  and  perhaps  some  pride  as  well ;  then  the 
ordinary  grease-cup  idlers  may  receive  the  attention  they  deserve.  But 
in  a  large  plant  with  many  conveyors  the  identity  and  importance  of 
separate  conveyors  are  lost.  To  fill  and  screw  up  grease  cups  regularly  and 
faithfully  in  such  a  place  calls  for  the  steady  work  of  one  or  more  men  and 
the  attention  which  these  men  give  to  their  work  greatly  influences  the 
cost  of  repairs,  the  cost  of  shut-downs  and  the  cost  of  carrying  a  ton  of 
material.  A  routine  job  of  that  kind  is  not  easy  to  supervise  and  conse- 
quently it  is  often  shirked.  * 

Roller  Bearing  Idlers  with  Oil  Lubrication. — A  still  greater  saving  of 
power  and  maintenance  may  be  expected  when  the  belt  is  carried  on  straight 
or  flared  idlers  and  when  the  roller  bearings  are  lubricated  with  oil,  as  shown 
in  Fig.  84.  The  oil  is  carried  in  the  base  of  the  bearing  and  at  a  low  level 
so  that  the  rollers  are  not  flooded;  oil  slings  prevent  leakage  along  the 
shaft,  there  are  fewer  moving  parts  and  those  are  of  light  weight,  and  all 
the  load  is  supported  by  the  roller  bearings.  In  multiple-pulley  idlers, 
however,  there  is  always  a  component  of  the  load  represented  by  end- 
thrust  on  pulley  hubs  which  cannot  be  taken  on  the  roller  bearings. 

The  covered  oil  well  shown  in  Fig.  84  permits  the  level  of  the  oil  to  be 
seen  quickly  and  when  new  oil  is  needed  it  can  be  put  in  easily.  It  must 
be  said,  however,  that  oil-lubricated  bearings  are  not  so  simple  as  those 
lubricated  with  grease,  and  in  the  type  of  bearing  with  a  lid  shown  in  Fig. 

95  it  is  not  easy  to  keep    the  oil    clean  when   the  conveyor  handles  fine 
material  or  works  in  a  dusty  place. 

On  the  application  of  improved  idlers  to  long-distance  conveying, 
see  p.  107. 


BELTS.  SUPPORTED  ON  RUNWAYS  95 

Idlers  with  Tapered  Roller  Bearings. — There  are  several  advantages  in 
the  tapered  roller  bearings  made'by  the  Timken  Roller  Bearing  Company 
(Canton,  Ohio)  and  others :  & 

1.  In  the  bores  of  inclined  troughing  pulleys,  the  axial  thrusts  are  taken 
on  the  hardened  roller  races  and  not  by  the  hubs  of  pulleys   or  separate 
washers. 

2.  The  inner  races  or  cones  are  tight  on  the  shaft  or  stud  and  the  latter 
does  not  turn,  hence  in  idlers  with  long  horizontal  shafts,  the  weight  of  the 
rotating  parts  is  less,  and  there  are  no  uncertainties  about  alignment  as  there 
may  be  when  the  pulley  is  tight  on  the  shaft  and  the  shaft  revolves  in  bearings. 

Belts  Supported  on  Runways. — The  use  of  a  smooth  runway  to  support 
a  loaded  belt  (see  Fig.  20)  is  now  obsolete,  so  far  as  handling  bulk  materials 
on  fabric  belts  is  concerned;  but  for  carrying  dishes,  bottles  and  some 
other  kinds  of  packaged  goods,  it  is  often  necessary  to  use  a  runway  in 
order  to  carry  the  goods  smoothly  and  without  danger  of  upsetting  them. 

If  the  loads  are  heavy  or  the  conveyor  long  the  friction  between  bel£ 
and  runway  may  be  too  wasteful  of  power  or  injurious  to  the  belt.  To 
lessen  this  friction,  it  has  been  suggested  (Plummer  patent  of  1911)  that  a 
separate  belt,  lubricated  on  the  inner  side,  be  used  between  the  carrying 
run  of  the  conveyor  belt  and  the  runway. 


CHAPTER   V 
DRIVING   THE   BELT 
Horse-power  to  Drive  Belt  Conveyors. — In  general, 

pull  in  pounds  X  speed  in  feet  per  minute 

horse-power  =h.p.  = — . 

33,000  foot-pounds  per  minute 

In  a  belt  conveyor  the  output  of  the  motor  is  expended  in  overcoming 
transmission  losses  up  to  the  conveyor-drive  pulley  and  in  putting  a  certain 
pull  in  the  belt.  The  transmission  losses  will  be  considered  later;  the  belt 
pull,  which  is  a  measure  of  the  horse-power  expended  within  the  conveyor, 
may  be  considered  as  made  up  of  several  items:  1.  The  friction  of  the  idler 
pulleys  in  revolving  under  the  weight  of  belt  and  material  carried;  2.  The 
bending  of  the  belt  over  the  idlers  and  over  the  end  pulleys;  3.  Getting  the 
material  up  to  speed  at  the  loading  point;  4.  The  lifting  and  slight  dis- 
turbance of  the  load  in  passing  over  the  idlers;  5.  The  friction  of  those 
shafts  which  are  driven  through  the  conveyor  belt,  such  as  foot  shafts, 
snub  shafts,  etc. 

Items  2,  3,  4  and  5  are,  as  a  rule,  relatively  small  in  amount,  and  it  is 
Difficult  to  determine  them;  the  usual  calculations  for  horse-power  assume 
a  value  of  item  1  large  enough  to  include  2,  3,  4  and  5  and  bring  values 
close  to  the  results  obtained  from  motor  readings  of  conveyors  in  actual 
service. 

On  this  assumption  the  horse-power  for  a  horizontal  belt  conveyor  is 

S      /idler  friction  due  to  empty  belt  \ 

<P'  "33.000  \4-idler  friction  due  to  material  carried  on  the  belt/ 


or 


where    L  =  length  of  conveyor  in  feet,  center  to  center; 
S  =belt  speed  in  feet  per  minute; 

X  =  weight  of  revolving  parts  of  idlers  per  1  foot  of  center  distance ; 
Y  =  weight  of  2  feet  of  empty  belt; 
Z  =  weight  of  material  on  1  foot  of  belt ; 
d=  diameter  of  idler  bearings; 
D=  diameter  of  idler  pulleys; 
/  =  coefficient  of  friction  in  bearings  of  idlers. 

96 


HORSE-POWER  TO  DRIVE  BELT  CONVEYORS 


97 


Experiments  with  conveyors  fitted  with  grease-lubricated  idlers  give 

=  .35  and  since  —  averages  .2}  we  say  /—  =  .07. 
L)  v  L) 

,     Tons  per  Hour  X2000       d_ 


2.33  T 


To  put  formula  (1)  in  handy  form,  X  and  Y  can  be  expressed  as  factors 
for  each  width  of  belt.  The  following  shows  the  method:  On  a  24-inch 
belt  the  pulleys  of  the  troughing  idlers  of  a  certain  make  weigh  40  pounds 
per  set,  and  at  an  average  spacing  of  4  feet  along  the  conveyor  they  weigh 
10  pounds  per  foot.  The  return  idlers  weigh  32  pounds  each,  or  about  3.2 

pounds  per  foot.  X  is  therefore  13.2  pounds  and  Xf—  =13.2  X.  07  =.93. 
A  24-inch  6-ply  belt  with  f-inch  cover  weighs  about  6  pounds  per  foot; 
therefore  7  =  12  and  Yf—  =  .84  pound.  Adding,  we  get  .93  +.84  =  1.77 

for  a  factor  which  represents  the  idler  friction  for  a  24-inch  empty  belt; 
calling  this  C,  we  can  say 


This  is  the  formula  given  by  Jeffrey.  Table  15  gives,  with  some  inter- 
polations, factors  C  calculated  by  Jeffrey  for  various,  widths  of  belt  on 
assumptions  of  weights  of  idlers  and  belts  similar  to  the  example  given  above. 
These  assumptions  cover  the  heaviest  belts  and  closest  spacing  of  idlers 
likely  to  be  used  for  the  various  widths. 

If  the  conveyor  is  inclined,  the  horse-power  required  to  lift  tons  per 
hour  =  T  through  a  vertical  height  =  H  in  feet  is 

T2000  H    _TH 
60X33,000~~990  ......... 

TABLE  15.—  DETERMINATION  OF  HORSE   POWER—  GREASE-LUBRICATED 

IDLERS 


Width 
of  Belt, 
In. 

C 

H.p. 
for 
Trip- 

Width 
of  Belt, 
In. 

C 

H.p. 
for 
Trip- 

Width 
of  Belt, 
In. 

C 

H.p. 
for 
Trip- 

Width 
of  Belt, 
In. 

C 

H.p. 
for 
Trip- 

per. 

per. 

per. 

per. 

12 

.65 

1 

22 

1.85 

1.5 

32 

2.80 

3 

42 

4.15 

4.5 

14 

.75 

1 

24 

2.00 

1.5 

34 

3.15 

3 

44 

4.35 

5 

16 

1.05 

1 

26 

2.15 

1.5 

36 

3.55 

3.5 

48 

4.75 

6 

18 

1.35 

1.5 

28 

2.30 

2 

38 

3.75 

3.5 

54 

5.50 

20 

1.70 

1.5 

30 

2.45 

2.5 

40 

3.95 

4 

60 

6.30 

The  inclination  of  the  belt  adds  nothing  to  the  power  required  to  drive  it 
empty,  since  the  downward  component  of  the  up-run  is  balanced  by  the 
downward  component  of  the  down-run.  There  is,  however,  an  added 
stress  in  the  belt  when  the  angle  exceeds  2°  or  4°  (see  p.  112  and  Table  22). 
The  horse-power  calculated  from  formulas  (2)  and  (3)  does  not  include 


98  DRIVING  THE  BELT 

losses  in  transmission  of  power  from  the  motor  to  the  drive  pulley.  To 
cover  these  losses  and  the  relatively  larger  percentage  of  friction  losses  in 
the  terminals  of  short  conveyors  it  is  customary  to  add  other  factors  to 
determine  the  total  horse-power  required  to  drive  the  conveyor.  The  follow- 
ing are  the  factors  as  given  by  Jeffrey:  Add  20  per  cent  for  conveyors 
under  50-foot  centers,  10  per  cent  for  50-  to  100-foot  centers  and  5  per  cent 
for  100-  to  150-foot  centers.  Add  for  each  belt  tripper  the  horse-power 
given  in  Table  15.  Add  5  per  cent  for  each  speed  reduction  between  drive 
pulley  and  line  shaft,  motor  or  engine,  when  chain  drive,  belt  drive  or  cut 
gears  are  used;  add  10  per  cent  for  each  reduction  through  rough-cast  gears. 
In  the  tables  published  by  C.  K.  Baldwin  (Marks,  M.  E.  Handbook, 

T\  T  J 

1st  ed.,  p.  1179)  formula  (1)  has  been  reduced  to  the  form  h.p.  = 

lOUu 

by  combining  into  one  term  the  three  terms  within  the  parenthesis.  This 
is  done  by  expressing  weights  of  idlers  and  weights  of  belt  in  terms  of  belt 
width  and  then  translating  them  into  terms  of  belt  capacity.  For  reason- 
able accuracy,  K  should  be  given  for  materials  of  various  weights,  since 
weight  of  material  determines  idler  spacing  and  belt  thickness.  The  line 
diagrams  published  by  Robins  are  based  on  the  Baldwin  formula  but  with 
lines  referring  to  materials  of  various  weights.  The  formula  of  the  Stephens- 
Adamson  Co.  is  of  the  same  form  but  with  numerical  factors  for  various 
weights  of  material  and  for  ball-bearing  and  also  grease-lubricated  idlers, 
the  ratio  of  the  factors  for  the  two  kinds  being  as  3  to  4. 

An  approximate  rule  often  used  for  horse-power  of  belt  conveyors  is  this : 
2  per  cent  of  the  tons  per  hour  for  every  100  feet  of  length  plus  1  per  cent 
of  the  tons  per  hour  for  every  10  feet  of  vertical  lift.  This  is, 

«> 


-    It  is  derived  from  equation  (1)  by  assuming  that  the  total  weight  of  belt 

W2q 
and  idler  parts  per  foot  centers  is  — -  where  W  =  belt  width  in  inches  and 

0=  weight  of  material  per  cubic  foot  in  pounds.     Then  since 

T  =^       (see  capacity  formula,  p.  144), 

X 1UO 


we  have 

T 


100  .0163' 

then  formula  (2)  becomes 

T         /  (\n  rr 

+2.33  T7)  =: 


33,000\.016  /        100   ' 

to  which  is  added  —       -  as  an  approximation  for  -  -  (see  formula  3). 
10  990 


HORSE-POWER  OF  GRAIN  CONVEYORS  99 

This  is  a  convenient  rule  and  one  easy  to  remember.  It  gives  results 
that  agree  closely  with  those  of  formula  (2)  for  materials  weighing  75 
pounds  per  cubic  foot.  For  materials  weighing  less  than  25  pounds  per 
cubic  foot  or  more  than  125  pounds  its  results  are  noticeably  different, 
being  smaller  for  light  materials  and  larger  for  heavy  materials  as  compared 
with  those  given  by  a  formula  like  (2),  where  the  horse-power  is  made  up 
of  the  sum  of  the  work  required  to  drive  the  conveyor  empty,  plus  that 
required  to  move  the  load.  It  must  be  said,  however,  that  for  light  materials 
formula  (2)  gives  results  that  are  rather  high,  since  the  factors  in  Table 
103-1  are  calculated  for  heavier  belts  and  closer  spacing  of  idlers  than 
would  be  used  for  materials  weighing  less  than  50  pounds  per  cubic  foot. 

Other  Formulas  for  Horse-power. — There  are  a  number  of  other  pub- 
lished formulas  for  horse-power  of  belt  conveyors,  but  instead  of  quoting 
them  with  their  tables  of  factors,  they  will  be  mentioned  briefly  as  follows: 

B.  F.  Goodrich  Rubber  Co.     Formula  (4)  (above). 

The  Goodyear  Tire  and  Rubber  Co.  A  formula  similar  to  (2),  but 
with  factors  referring  to  tonnage  and  belt  weight  only. 

Link-Belt  Company.  A  series  of  tables  based  on  a  formula  like  (1), 
but  with  factors  added  to  cover  friction  losses  at  the  conveyor  terminals. 

Main  Belting  Co.  Tables  based  on  a  formula  similar  to  (2)  giving 
separate  values  for  empty  conveyors  and  for  the  loads  carried. 

Robins  Conveying  Belt  Co.  A  line  diagram  which  gives  results  similar 
to  the  Baldwin  formula  (see  p.  98). 

Stephens-Adamson    Manufacturing    Co.     A    comprehensive    formula, 

/"K  T  -i-  T-f  \ 

^.^.  -  . —  X  TJD  \  +  P,  and  with  tables  to  supply  the  necessary  fac- 

\     990  / 

tors  K,  J,  D  and  P. 

Table  16  gives  a  comparison  of  seven  rules  for  the  horse-power  of 
belt  conveyors  as  applied  to  nine  specific  cases,  using  in  the  calculation  for 
each  rule  the  belt  capacity  as  given  by  the  authority  for  the  rule. 

Horse-power  of  Grain  Conveyors. — A  formula  in  use  for  the  horse- 
power of  horizontal  grain  conveyors  is  -fo  horse-power  per  1000  bushels 
per  hour  per  100  feet  of  distance.  For  wheat,  which  weighs  60  pounds 
per  bushel,  this  is  the  same  as  that  given  by  formula  (4) — i.e.,  h.p.  =2  per 
cent  of  the  tons  per  hour  per  100  feet  of  distance  traveled. 

Tables  Based  on  Formulas  (2)  and  (3). — Formulas  (2)  and  (3)  with 
Table  15  give  all  that  is  necessary  to  calculate  horse-power  when  L, 
S,  T  and  H  are  known.  It  is,  however,  convenient  at  times  to  have  the 
results  of  calculations  set  down  in  the  form  of  tables,  and  since  formula  (2) 

indicates  by  separate  terms  the  horse-power  for  the  empty  belt  and  the 

r<QT 

horse-power  for  the  material  conveyed,  Table  17  gives  values  for  — — — 

oo,OUU 

for  the  empty  belt  for  conveyors  of  various  widths  and  lengths  for  a  speed 

o 

of  100  feet  per  minute.     For  other  speeds  multiply  by  — ;  for  other  lengths, 


100 


DRIVING  THE  BELT 


ll 

CO  <j 


M 


« 


§ 


u 


O 


o 


2s 


•8  1 


00 

CO 


^  o 


a 


1  S 


' 


a  ft 


s 


Sa 

JS  d 

Jib 


• 

„  o 

i* 

.    0 


^  ft 


TABLES 


101 


3 


S  '  -° 

8  s  ~ 

t»  ^  2 

§  i  I 

H  1  ^ 

K"  W  ^ 

^  e  ^ 

P  ^  g. 


s£ 

w 

PQ 

g 


02 


0 


^  ^H  ,H  (N  (N  (N  (N  <N  CO  CO  Tt<  TJH  Tf         1C  C£3 


<N<N<N<NCOCOCOCOTt<iO 


(M(M(N(N<NCOCO-^ 


"i" 


Hi,aiA\. 


102 


DRIVING  THE  BELT 


TABLE  18.— HORSE-POWER— HORIZONTAL  BELT 

(For  Empty  Conveyor 


MATERIAL  PER  HOUR  IN  TONS  (2000  POUNDS) 

Tons 
per 
Hour 

LENGTH  OF  CONVEYOR  — 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

125 

150 

175 

5 
10 
15 

.05 
.05 
.05 

.05 
.05 
.05 

.05 
.05 
.05 

.05 
.05 
.06 

.05 
.05 
.06 

.05 
.05 
.08 

.05 
.06 
.08 

.05 
.07 
.10 

.05 
.07 
.11 

.05 

.08 
.12 

.05 
.10 
.15 

.06 

.12 

.18 

.07 
.13 
.19 

20 
25 
30 
35 

.05 
.05 
.05 
.05 

.05 
.05 
.06 
.07 

.05 
.06 
.08 
.09 

.07 
.08 
.10 
.12 

.08 
.10 
.12 

.14 

.10 
.12 
.15 

.17 

.12 

.14 
.17 
.21 

.13 
.16 
.20 
.23 

.14 
.17 
.21 
.24 

.15 
.19 
.23 
.27 

.20 
.15 
.29 
.34 

.23 
.29 
.34 
.40 

.26 
.32 
.39 
.45 

40 
45 
50 
55 

.05 
.05 
.05 
.06 

.08 
.09 
.09 
.10 

.10 
.12 
.13 

.14 

.14 
.15 
.17 

.18 

.16 
.18 
.20 
.22 

.19 
.22 
.24 

.27 

.23 
.26 

.28 
.31 

.26 
.29 
.32 
.36 

.28 
.31 
.35 
.39 

.30 
.34 
.38 
.42 

.38 
.43 

.47 
.52 

.45 
.51 
.56 
.62 

.52 

.58 
.64 
.70 

60 
65 
70 
75 

.06 

.07 
.07 
.08 

.11 
.12 
.13 
.14 

.15 

.17 

.18 
.19 

.20 
.22 
.23 
.25 

.24 
.26 
.28 
.30 

.29 
.32 
.34 
.37 

.34 
.37 
.40 
.43 

.39 

.42 
.45 
.49 

.42 
.46 
.49 
.52 

.45 
.49 
.53 
.57 

.57 
.62 
.66 
.71 

.68 

.74 
.79 

.85 

.77 
.83 
.90 
.96 

80 
85 
90 
95 

.08 
.09 
.09 
.10 

.15 

.16 
.17 

.18 

.20 
.21 
.23 
.24 

.27 
.29 
.30 
.32 

.32 
.34 
.36 
.38 

.39 
.42 
.44 
.46 

.45 

.48 
.51 
.54 

.52 
.55 

.58 
.62 

.56 
.60 
.63 
.67 

.60 
.64 

.68 

.72 

.76 
.81 

.85 
.89 

.90 
.95 
1.01 
1.06 

1.03 
1.09 
1.16 
1.22 

100 
125 
150 
175 

.10 
.13 
.15 

.18 

.18 
.23 

.27 
.32 

.25 
.31 
.38 
.44 

.33 

.41 
.50 

.58 

.40 
.50 
.60 
.70 

.48 
.60 
.72 

.84 

.56 
.70 
.84 
.98 

.64 
.80 
.96 
1.12 

.70 
.88 
1.05 
1.23 

.75 
.94 
1.13 
1.32 

.94 
1.18 
1.41 
1.65 

1.12 
1.40 
1.68 
1.96 

1.28 
1.60 
1.92 
2  24 

200 
225 
250 
275 

.20 
.23 
.25 

.28 

.36 
.41 
.45 
.50 

.50 
.56 
.63 
.69 

.66 
.75 
.83 
.91 

.80 
.90 
1.00 
1.10 

.96 
1.08 
1.20 
1.32 

1.12 
1.26 
1.40 
1.54 

1.28 
1.44 
1.60 

1.76 

1.40 
1.58 
1.75 
1.93 

1.50 
1.69 
1.88 
2.06 

1.88 
2.12 
2.35 
2  59 

2.24 
2.52 
2.80 
3.08 

2.56 

2.88 
3.20 
3.54 

300 
325 
350 
375 

.30 
.33 
.35 

.38 

.54 
.59 
.63 
.68 

.75 

.81 
.87 
.93 

.99 
1.07 
1.15 
1.24 

1.20 
1.30 
1.40 
1.50 

1.44 
1.56 
1.68 
1.80 

1.68 
1.82 
1.96 
2.10 

1.92 
2.08 
2.24 
2.40 

2.10 
2.28 
2.45 
2.63 

2.25 
2.44 
2.63 
2.81 

2.82 
3.06 
3.29 
3.53 

3.36 
3.64 
3.92 
4.20 

3.84 
4.16 

4.48 
4.80 

400 
425 
450 
475 

.40 
.43 
.45 

.43 

.72 
.77 
.81 
.86 

.00 
.06 
.12 

.18 

1.32 
1.41 
1.48 
1.56 

1.60 
1.70 
1.80 
1.90 

1.92 
2.04 
2.16 

2.28 

2.24 
2.38 
2.52 
2.66 

2.56 
2  ^^ 
2.88 
3.04 

2.80 
2.98 
3.15 
3.33 

3.00 
3.18 
3.37 
3.56 

3.76 
4.00 
4.23 

4.47 

4.48 
4.76 
5.04 
5.32 

5.12 
5.44 
5.76 
6.08 

500 
600 
700 
800 
900 
1000 

.50 
.60 
.70 
.80 
.90 
1.00 

.90 
1.08 
1.26 
1.44 
1.62 
1.80 

.25 
.50 
1.75 
2.00 
2.25 
2.50 

1.65 
1.98 
2.31 
2.64 
2.97 
3.30 

2.00 
2.40 
2.80 
3.20 
3.60 
4.00 

2.40 
2.88 
3.36 
3.84 
4.32 
4.80 

2.80 
3.36 
3.92 
4.48 
5.04 
5.60 

3.20 
3.84 

4.48 
5.12 
5.76 
6.40 

3.50 
4.20 
4.90 
5.60 
6.30 
7.00 

3.75 
4.50 
5.25 
6.00 
6.75 
7.50 

4.70 
5.64 
6.58 
7.52 
8.46 
9.40 

5.60 
6.72 
7.84 
8.96 
10.08 
11.20 

6.40 
7.68 
8.96 
10.24 
11.52 
12.80 

TABLES  BASED  ON  FORMULAS 


103 


CONVEYORS— FOR  MATERIAL  ONLY 

See  Table  17)  »  '" 


FEET — CENTER  TO  CENTER 


200 

225 

250 

275 

300 

325 

350 

375 

400 

425 

450 

475 

500 

.07 

.08 

.09 

.10 

.11 

.12 

.13 

.14 

.15 

.16 

.16 

.17 

.18 

.14 

.16 

.18 

.20 

.22 

.24 

.25 

.27 

.29 

.31 

.32 

.34 

.36 

.21 

.24 

.27 

.30 

.33 

.36 

.38 

.40 

.43 

.46 

.48 

.51 

.54 

.28 

.32 

.36 

.40 

.43 

.47 

.50 

.54 

.58 

.61 

.65 

.68 

.72 

.36 

.40 

.45 

.49 

.54 

.59 

.63 

.68 

.72 

.76 

.81 

.85 

.90 

.43 

.48 

.54 

.59 

.65 

.70 

.75 

.81 

.86 

.92 

.97 

1.02 

1.08 

.50 

.56 

.63 

.69 

.76 

.82 

.88 

.9*5 

1.00 

1.07 

1.13 

1.19 

1.26 

.57 

.64 

.72 

.79 

.86 

.93 

.00 

.08 

1.15 

1.22 

1.29 

1.36 

1.44 

.64 

.72 

.81 

.89 

.97 

1.05 

.13 

.21 

1.29 

1.37 

1.45 

1.53 

1.61 

.71 

.80 

.89 

.98 

1.07 

1.16 

.25 

.34 

1.43 

1.52 

1.61 

1.70 

1.79 

.78 

.88 

.98 

1.08 

1.18 

1.28 

.38 

.48 

1.57 

1.68 

1.77 

1.87 

1.97 

.85 

.96 

1.07 

.18 

1.29 

1.40 

.50 

.61 

1.72 

1.83 

1.93 

2.04 

2.15 

.93 

.04 

1.16 

.28 

1.40 

1.52 

.63 

.75 

1.86 

1.98 

1.20 

2.21 

2.33 

1.00 

.12 

1.25 

.38 

1.50 

1.64 

1.75 

.88 

2.00 

2.13 

2.26 

2.38 

2.51 

1.07 

.20 

1.34 

.47 

1.61 

1.75 

1.88 

2.01 

2.14 

2.28 

2.42 

2.55 

2.69 

1.14 

.28 

1.43 

.57 

1.72 

1.86 

2.00 

2.15 

2.29 

2.43 

2.58 

2.72 

2.86 

1.21 

.36 

1.51 

.67 

1.83 

1.98 

2.13 

2/29 

2.43 

2.59 

2.74 

2.89 

3.04 

1.28 

.44 

1.60 

.77 

1.94 

2.09 

2.25 

2.42 

2.58 

2.74 

2.90 

3.06 

3.22 

1.35 

.52 

1.69 

.87 

2.04 

2.21 

2.38 

2.55 

2.72 

2.89 

3.06 

3.23 

3.40 

1.42 

1.60 

1.78 

1.96 

2.14 

2.32 

2.50 

2.68 

2.86 

3.04 

3.22 

3.40 

3.58 

1.78 

2.00 

2.23 

2.45 

2.68 

2.90 

3.13 

3.35 

3.58 

3.80 

4.03 

4.25 

4.48 

2.13 

2.40 

2.67 

2.94 

3.21 

3.48 

3.75 

4.02 

4.29 

4.56 

4.83 

5.10 

5.37 

2.49 

2.80 

3.12 

3.43 

3.75 

4.06 

4.38 

4.69 

5.01 

5.28 

5.64 

5.95 

6.27 

2.84 

3.20 

3.56 

3.92 

4.28 

4.64 

5.00 

5.36 

5.72 

6.08 

6.44 

6.80 

7.16 

3.20 

3.60 

4.01 

4.41 

4.82 

5.22 

5.63 

6.03 

6.44 

6.84 

7.25 

7.65 

8.06 

3.55 

4.00 

4.45 

4.90 

5.35 

5.80 

6.25 

6.70 

7.15 

7.60 

8.05 

8.50 

8.95 

3.91 

4.40 

4.90 

5.39 

5.89 

6.38 

6.88 

7.37 

7.87 

8.36 

8.86 

9.35 

9.85 

4.26 

4.80 

5.34 

5.88 

6.42 

6.96 

7.50 

8.04 

8.58 

9.12 

9.66 

10.20 

10.74 

4.62 

5.20 

5.89 

6.37 

6.96 

7.54 

8.13 

8.71 

9.30 

9.88 

10.47 

11.05 

11.64 

4.97 

5.60 

6.33 

6.86 

7.50 

8.12 

8.76 

9.38 

10.01 

10.64 

11.27 

11.90 

12.53 

5.33 

6.00 

6.78 

7.35 

8.03 

8.70 

9.38 

10.05 

10.73 

11.40 

12.07 

12.75 

13.43 

5.68 

6.40 

7.12 

7.84 

8.56 

9.28 

10.00 

10.72 

11.44 

12.16 

12.88 

13.60 

14.32 

6.04 

6.80 

7.57 

8.33 

9.09 

9.86 

10.63 

11.39 

12.16 

12.92 

13.69 

14.45 

15.22 

6.39 

7.20 

8.01 

8.82 

9.63 

10.44 

11.25 

12.06 

12.87 

13.68 

14.49 

15.30 

16.11 

6.75 

7.60 

8.46 

9.31 

10.16 

11.02 

11.88 

12.73 

13.59 

14.44 

15.30 

16.15 

17.01 

7.10 

8.00 

8.90 

9.80 

10.70 

11.60 

12.50 

13.40 

14.30 

15.20 

16.10 

17.00 

17.90 

8.52 

9.60 

10.68 

11.76 

12.84 

13.92 

15.00 

16.08 

17.16 

18.24 

19.32 

20.40 

21.48 

9.94 

11.20 

12.46 

13.72 

14.98 

16.24 

17.50 

18.76 

20.02 

21.28 

22.54 

23.80 

25.06 

11.36 

12.80 

14.24 

15.68 

17.12 

18.56 

20.00 

21.44 

22.88 

24.32 

25.76 

27.20 

28.64 

12.78 

14.40 

16.02 

17.64 

19.26 

20.88 

22.50 

24.12 

25.74 

27.36 

28.98 

30.60 

32.22 

14.20 

16.00 

17.80 

19.60 

21.40 

23.20 

25.00 

26.80 

28.60 

30.40 

32.20 

34.00 

35.80 

104 


DRIVING  THE  BELT 


TABLK  19.— HORSE-POWER  TO  LIFT  MATE 
(For  Horse-power  for  Level  Conveyor 


HEIGHT  OF  VERTICAL 

5 

10 

15 

20 

25 

30 

35 

40 

45 

50 

55 

60 

5 

.03 

.06 

.09 

.11 

.14 

.16 

.19 

.21 

.24 

.26 

.29 

.31 

10 

.06 

.11 

.16 

.21 

.26 

.31 

.36 

.41 

.46 

.51 

.56 

.61 

15 

.09 

.16 

.24 

.31 

.39 

.46 

.54 

.61 

.69 

.76 

.84 

.92 

20 

.11 

.21 

.31 

.41 

.51 

.61 

.71 

.81 

.91 

1.01 

1.11 

1.22 

25 

.14 

.26 

.39 

.51 

.64 

.76 

.89 

1.02 

1.15 

1.27 

1.40 

1.52 

30 

.16 

.31 

.46 

.61 

.76 

.91 

1.06 

1.22 

1.37 

1.52 

1.67 

1.82 

35 

.19 

.36 

.54 

.71 

.*9 

1.06 

1.25 

1.42 

1.60 

1.77 

1.95 

2.13 

40 

.21 

.41 

.61 

.81 

1.02 

1.22 

1.42 

1.62 

1.82 

2.02 

2.22 

2.43 

45 

.24 

.46 

.69 

.91 

1.15 

1.37 

1.60 

1.82 

2.05 

2.28 

2.51 

2.73 

50 

.26 

.51 

.76 

1.01 

1.27 

1.52 

1.77 

2.02 

2.28 

2.53 

2.78 

3.03 

55 

.29 

.56 

.84 

1.11 

1.40 

1.67 

1.95 

2.22 

2.51 

2.78 

3.06 

3.34 

^ 

60 

.31 

.61 

.92 

1.22 

1.52 

1.82 

2.13 

2.43 

2.73 

3.03 

3.34 

3.64 

1 

65 

.34 

.66 

1.00 

1.32 

1.65 

1.97 

2.31 

2.63 

2.96 

3.28 

3.62 

3.94 

70 

.36 

.71 

1.07 

1.42 

1.78 

2.13 

2.48 

2.83 

3.19 

3.54 

3.90 

4.25 

§ 

75 

.39 

.76 

1.15 

1.52 

1.91 

2.28 

2.66 

3.03 

3.42 

3.79 

4.18 

4.55 

£3 

80 

.41 

.81 

1.22 

1.62 

2.03 

2.43 

2.84 

3.24 

3.64 

4.04 

4.45 

4.85 

1 

85 

.44 

.86 

1.30 

1.72 

2.16 

2.58 

3.02 

3.44 

3.87 

4.29 

4.73 

5.15 

& 

90 

.46 

.91 

1.37 

1.82 

2.28 

2.73 

3.19 

3.64 

4.10 

4.55 

5.01 

5.46 

2 

95 

.49 

.96 

1.45 

1.92 

2.41 

2.88 

3.37 

3.84 

4.33 

4.80 

5.29 

5.70 

« 
p 

100 

.51 

1.01 

1.52 

2.02 

2.53 

3.03 

3.54 

4.04 

4.55 

5.05 

5.56 

6.06 

o 

125 

.64 

1.27 

1.90 

2.53 

3.16 

3.79 

4.43 

5.05 

5.69 

6.32 

6.95 

7.58 

W 

150 

.76 

1.52 

2.28 

3.03 

3.79 

4.55 

5.31 

6.06 

6.82 

7.58 

8.34 

9.09 

K 
H 
EL, 

175 

.89 

1.78 

2.66 

3.54 

4.42 

5.31 

6.20 

7.07 

7.96 

8.85 

9.73 

10.61 

J 

a 

200 

1.01 

2.02 

3.03 

4.04 

5.05 

6.06 

7.07 

8.08 

9.09 

10.10 

11.11 

12.12 

K 

225 

1.14 

2.28 

3.41 

4.55 

5.68 

6.81 

7.96 

9.09 

10.23 

11.37 

12.50 

13.64 

g 

250 

1.27 

2.53 

3.79 

5.05 

6.32 

7.58 

8.84 

10.10 

11.37 

12.63 

13.89 

15.15 

<! 

275 

1.40 

2.79 

4.17 

5.56 

6.95 

8.34 

9.73 

11.11 

12.51 

13.90 

15.28 

16.67 

300 

1.52 

3.03 

4.55 

6.06 

7.58 

9.09 

10.61 

12.12 

13.64 

15.15 

16.67 

18.18 

325 

1.65 

3.29 

4.93 

6.57 

8.21 

9.85 

11.50 

13.13 

14.78 

16.42 

18.06 

19.70 

350 

1.77 

3.54 

5.30 

7.07 

8.84 

10.61 

12.37 

14.14 

15.91 

17.68 

19.44 

21.21 

375 

1.90 

3.80 

5.68 

7.58 

9.47 

11.37 

13.26 

15.15 

17.05 

18.95 

20.83 

22.73 

400 

2.02 

4.04 

6.06 

8.08 

10.10 

12.12 

14.14 

16.16 

18.18 

20.20 

22.22 

24.24 

425 

2.15 

4.30 

6.44 

8.59 

10.73 

12.88 

15.03 

17.17 

19.32 

21.47 

23.61 

25.76 

450 

2.28 

4.55 

6.82 

9.09 

11.37 

13.64 

15.92 

18.18 

20.46 

22.73 

25.00 

27.27 

475 

2.41 

4.80 

7.20 

9.60 

12.00 

14.40 

16.80 

19.19 

21.60 

24.00 

26.39 

28.79 

500 

2.53 

5.05 

7.58 

10.10 

12.63 

15.15 

17.68 

20.20 

22.73 

25.25 

27.78 

30.30 

600 

3.03 

6.06 

9.09 

12.12 

15.15 

18.18 

21.21 

24.24 

27.27 

30.30 

33.33 

36.36 

700 

3.53 

7.07 

10.60 

14.14 

17.67 

21.21 

24.74 

28.28 

31.81 

35.35 

38.88 

42.42 

800 

4.04 

8.08 

12.12 

16.16 

20.20 

24.24 

28.28 

32.32 

36.36 

40.40 

44.44 

48.48 

900 

4.55 

9.09 

13.64 

18.18 

22.73 

27.27 

32.82 

36.36 

40.91 

45.45 

50.00 

54.54 

1000 

5.05 

10.10 

15.15 

20.20 

25.25 

30.30 

35.35 

40.40 

45.45 

50.50 

55.55 

60.60 

TABLES  BASED  ON  FORMULAS 


105 


RIALS  ON  INCLINED  BELT  CONVEYORS 

See  Tables  17  and  18)  *    " 


LIFT  IN  FEET 


65 

70 

75 

80 

85 

90 

95 

100 

110 

120 

130 

140 

150 

.34 

.36 

.39 

.41 

.44 

.46 

.49 

.51 

.56 

.61 

.66 

.71 

.76 

.66 

.71 

.76 

.81 

.86 

.91 

.96 

1.01 

1.12 

1.22 

1.32 

1.42 

1.52 

1.00 

1.07 

1.15 

1.22 

1.30 

1.37 

1.45 

1.52 

1.68 

1.83 

1.98 

2.13 

2.28 

1.32 

1.42 

1.52 

1.62 

1.72 

1.82 

1.92 

2.02 

2.23 

2.43 

2.63 

2.83 

3.03 

1.65 

1.78 

1.91 

2.03 

2.16 

2.28 

2.41 

2.53 

2.78 

3.04 

3.29 

3.54 

3.79 

1.97 

2.13 

2.28 

2.43 

2.58 

2.73 

2.88 

3.03 

3.34 

3.64 

3.94 

4.25 

4.55 

2.31 

2.48 

2.66 

2.84 

3.02 

3.19 

3.37 

3.54 

3.90 

4.25 

4.60 

4.96 

5.31 

2.63 

2.83 

3.03 

3.24 

3.44 

3.64 

3.84 

4.04 

4.45 

4.85 

5.26 

5.66 

6.06 

2.96 

3.19 

3.42 

3.64 

3.87 

4.10 

4.33 

4.55 

5.01 

5.46 

5.92 

6.37 

6.82 

3.28 

3.54 

3.79 

4.04 

4.29 

4.55 

4.80 

5.05 

5.56 

6.06 

6.57 

7.07 

7.58 

3.62 

3.90 

4.18 

4.45 

4.73 

5.01 

5.29 

5.56 

6.12 

6.67 

7.23 

7.68 

8.34 

3.94 

4.25 

4.55 

4.85 

5.15 

5.46 

5.70 

6.06 

6.67 

7.28 

7.88 

8.49 

9.09 

4.28 

4.60 

4.93 

5.26 

5.59 

5.92 

6.25 

6.57 

7.23 

7.89 

8.54 

9.20 

9.85 

4.60 

4.95 

5.31 

5.66 

6.01 

6.37 

6.72 

7.07 

7.78 

8.49 

9.20 

9.91 

10.61 

4.93 

5.31 

5.69 

6.07 

6.45 

6.83 

7.21 

7.58 

8.34 

9.10 

9.86 

10.62 

11.37 

5.26 

5.66 

6.07 

6.47 

6.88 

7.28 

7.68 

8.08 

8.89 

9.70 

10.51 

11.32 

12.12 

5.59 

6.01 

6.45 

6.88 

7.31 

7.74 

8.17 

8.59 

9.45 

10.31 

11.17 

12.03 

12.88 

5.92 

6.37 

6.83 

7.28 

7.74 

8.19 

8.64 

9.09 

10.00 

10.91 

11.82 

12.73 

13.64 

6.25 

6.27 

7.21 

7.68 

8.17 

8.64 

9.12 

9.60 

10.56 

11.52 

12.48 

13.44 

14.40 

6.57 

7.07 

7.58 

8.08 

8.59 

9.09 

9.60 

10.10 

11.11 

12.12 

13.13 

14.14 

15.15 

8.12 

8.84 

9.48 

10.10 

10.74 

11.37 

12.00 

12.63 

13.89 

15.15 

16.42 

17.68 

18.96 

9.85 

10.61 

11.37 

12.12 

12.88 

13.64 

14.40 

15.15 

16.67 

18.18 

19.70 

21.22 

22.74 

11.50 

12.38 

13.27 

14.14 

15  .  03 

15.92 

16.80 

17.68 

19.45 

21.21 

22.98 

24.75 

26.54 

13.13 

14.14 

15.15 

16.16 

17.17 

18.18 

19.19 

20.20 

22.22 

24.24 

26.26 

28.28 

30.30 

14.78 

15.91 

17.05 

18.18 

19.32 

20.46 

21.59 

22.73 

25.00 

27.27 

29.55 

31.82 

34.10 

16.42 

17.68 

18.94 

20.20 

21.47 

22.73 

24.49 

25.25 

27.78 

30.30 

32.83 

35.35 

37.88 

18.07 

19.45 

20.84 

22.22 

23.62 

25.01 

26.89 

27.78 

30.56 

33.33 

36.11 

38.89 

41.68 

19.70 

21.21 

22.73 

24.24 

25.74 

27.27 

28.79 

30.30 

33.33 

36.36 

39.39 

42.42 

45.45 

20.35 

22.98 

24.63 

26.26 

27.89 

29.55 

31.19 

32.73 

36.11 

39.39 

42.68 

45.94 

49.26 

22.98 

24.75 

26.51 

28.28 

30.10 

31.82 

33.58 

35.35 

38.89 

42.42 

45.96 

49.49 

53.03 

24.63 

26.47 

28.41 

30.30 

32.15 

34.10 

35.98 

37.87 

41.67 

45.45 

49.24 

53.03 

56.82 

26.26 

28.28 

30.30 

32.32 

34.34 

36.36 

38.38 

40.40 

44.44 

48.48 

52.52 

56.56 

60.60 

27.91 

30.05 

32.20 

34.34 

36.49 

38.64 

40.78 

42.93 

47.22 

51.51 

55.80 

60.09 

64.40 

29.54 

31.82 

34.09 

36.36 

38.64 

40.92 

43.18 

45.45 

50.00 

54.54 

58.09 

63.63 

68.18 

31.19 

33.59 

35.99 

38.38 

40.79 

43.20 

45.58 

47.98 

52.78 

57.57 

62.37 

67.16 

71.98 

32.83 

35.35 

37.87 

40.40 

42.93 

45.45 

48.98 

50.50 

55.55 

60.60 

65.65 

70.70 

75.75 

39.39 

42.42 

45.45 

48.48 

51.51 

54.54 

57.57 

60.60 

66.66 

72.72 

78.78 

84.84 

90.90 

45.95 

49.49 

53.02 

56.56 

60.19 

63.63 

67.16 

70.70 

77.77 

84.84 

91.91 

98.98 

106.05 

52.52 

56.56 

60.60 

64.64 

68.68 

72.72 

76.76 

80.80 

88.88 

96.96 

105.04 

113.12 

121.20 

59.09 

63.63 

68.18 

72.72 

77.27 

81.81 

86.36 

90.90 

100.00 

109.08 

118.17 

127.26 

136.35 

65.65 

70.70 

75.75 

80.80 

85.85 

90.90 

95.95 

101.01 

111.11 

121.21 

131.31 

141.41 

151.51 

j 

106  DRIVING  THE  BELT 

interpolate.     The  values  given  include  the  factors  required  for  conveyors 
shorter  than  150-foot  centers.     In  a  similar  way  Table  18  gives  values  for 
*)  ^*3  T  T 
-  for  the  material  carried  on    conveyors  of  various    capacity  and 

length,  including  the  factors  required  for  conveyors  shorter  than  150-foot 
centers.  For  capacities  or  lengths  not  given  in  the  table,  interpolate. 

For  a  level  or  horizontal  conveyor,  add  the  values  taken  from  Table  1  7 
and  Table  18.  For  an  inclined  conveyor,  add  to  the  sum  of  these,  the 
horse-power  taken  from  Table  19  which  is  based  on  formula  (3),  page  97. 

Horse-power  of  Conveyors  with  Improved  Idlers.  —  Laboratory  tests  of 
troughed-belt  idlers  of  various  kinds  show  that  the  coefficient  of  friction 
falls  off  when  the  bearings  are  lubricated  by  oil,  and  that  it  is  still  lower 
when  roller  bearings  or  ball  bearings  are  used.  The  comparative  values  are 
about  as  follows: 

Coefficient  of  friction,  grease-lubricated  idlers  .  .  100  per  cent 
Coefficient  of  friction,  oil-lubricated  idlers  .....  60  per  cent 
Coefficient  of  friction,  roller-bearing  idlers  .....  26  per  cent 

This  does  not  mean  that  when  a  conveyor  is  equipped  with  oil-lubricated 
bearings,  for  instance,  that  the  horse-power  will  be  60  per  cent  of  that  given 
by  formula  (2)  or  that  (100—26)  =74  per  cent  of  power  will  be  saved  by 
using  roller-bearing  idlers.  The  reason  is  that  the  coefficients  used  in  the 
derivation  of  that  formula  include,  as  has  been  stated  on  page  96,  not 
only  friction  in  the  idler  bearings,  but  also  several  other  factors  which  are 
external  to  the  idlers  and  which  will  remain  in  spite  of  improvements  in  the 
idlers. 

There  is  no  doubt  that  considerable  power  is  saved  in  long  conveyors 
by  using  idlers  with  ball  or  roller  bearings,  or  even  oil  bearings,  but  there 
are  no  available  records  of  direct  comparative  tests.  Statements  by  manu- 
facturers are  given  in  Chapter  IV,  and  some  comparisons  have  been  made 
between  the  actual  horse-power  required  for  conveyors  equipped  with 
ball  or  roller  bearings  and  the  horse-power  which  it  is  estimated  these 
conveyors  would  have  taken  had  they  been  fitted  with  grease-lubricated 
idlers.  Several  comparisons  of  that  kind  are  given  in  Chapter  IV. 

If  a  horse-power  formula  were  developed  in  which  the  idler  losses  were 
treated  separately  from  the  other  losses  —  namely,  bending  the  belt,  speeding 
up  material  at  the  loading  point,  lifting  the  load  over  the  idlers  and  the 
losses  in  the  conveyor  terminals,  then  it  would  be  possible  to  say  what 
power  could  be  saved  by  better  idlers.  Unfortunately,  however,  there  are 
no  data  available  to  establish  such  a  formula. 

An  empirical  formula  which  agrees  well  with  tests  of  the  three  con- 
veyors referred  to  on  page  92,  and  with  tests  of  a  number  of  long  conveyors 
36  inches  or  more  in  width,  fitted  with  ball-bearing  idlers  (p.  90),  is 

OlffX       ....... 


V    100          10 


LONG-DISTANCE  BELT  CONVEYING  107 

This  is  in  the  form  of  formula  (4).  Compared  with  (4),  it  shows  that  the 
horse-power  required  for  conveying,  exclusive  of  the  lift,  is,  with  roller- 
bearing  or  ball-bearing  idlers  in  ggod  condition,  a  little  less  than  half  that 
required  for  plain  troughing  pulleys  with  grease  lubrication. 

Long-distance  Belt  Conveying — From  formula  (4)  (p.  98)  it  is  apparent 
that  in  a  level  belt  conveyor  where  //  =0,  1  h.p.  will  convey  1  ton  per  hour 
a  distance  of  5000  feet  over  plain  grease-lubricated  idlers,  or,  roughly,  1  h.p.- 
hour  will  convey  1  ton  1  mile.  On  the  basis  of  power  consumption  alone 
a  belt  conveyor  that  carries  1  ton  1  mile  in  one  hour  is  not  so  economical 
as  a  horse  and  cart,  and  for  handling  large  quantities  of  material  over  long 
distances  a  train  of  cars  drawn  by  a  steam  or  electric  locomotive  will  require 
much  less  power  than  a  belt  or  a  series  of  belts.  To  buy  belts  with  their 
carrying  idlers  and  driving  machinery  and  build  a  structure  to  support 
the  conveyor  will  generally  cost  more  in  such  cases  than  to  lay  track  and 
provide  cars  and  motive  power  suited  to  the  quantity  of  material  to  be 
handled. 

There  are,  however,  conditions  in  which  a  long  belt  system  may  cost  so 
much  less  for  operating  labor  and  attendance  than  a  car  system  that  it  will 
pay  to  install  the  belt  conveyors.  For  example,  an  important  mining 
company  had  under  consideration  for  several  years  a  plan  to  carry  8500 
tons  of  coal  per  day  from  three  inland  mines  to  a  shipping  point  on  a  river 
over  four  miles  away.  The  choice  lay  between  mine-car  haulage  with 
electric  locomotives  on  the  one  hand  and  a  belt  conveyor  system  on  the  other. 

From  costs  derived  by  the  company  from  the  operation  of  many  haulage 
plants  and  several  large  belt  conveyors,  comparative  estimates  were  made 
which  showed:  1.  The  total  cost  of  installation  of  the  belt  conveyor  system 
was  about  25  per  cent  below  that  of  the  haulage  system,  and  the  annual 
charge  for  interest  was  correspondingly  less.  2.  The  annual  charge  for 
depreciation  for  the  conveyor  system  was  about  15  per  cent  higher;  this 
was  based  on  an  estimated  life  of  three  years  for  belts,  five  years  for  idlers, 
fifteen  years  (average)  for  other  machinery,  thirty  years  for  steel  and 
concrete  work.  3.  The  estimated  power  cost  for  the  belts  was  double 
that  for  the  haulage.  4.  The  probable  cost  of  labor  and  attendance  for 
the  belt  system  was  about  half  the  corresponding  charge  for  the  car  system. 
This  one  item  showed  a  difference  of  about  $85.000  between  the  annual 
operating  costs  and  when  balanced  with  the  other  items  mentioned,  it 
was  sufficient  to  show  an  estimated  saving  of  over  three  cents  per  ton  of 
coal  carried. 

As  a  result  of  this  comparison  it  was  decided  to  install  the  belt  system, 
and  the  work  is  now  under  construction  (1922).  The  distance  from  the 
loading  station  in  the  mine  to  the  bin  at  the  river  is  23,500  feet,  and  the 
total  rise  is  about  200  feet.  The  conveyors,  20  in  number,  will  be  entirely 
underground  in  existing  mine  passages  which  have  been  widened  and 
straightened  for  the  purpose.  The  idlers  will  be  fitted  with  roller  bearings 
or  ball  bearings.  From  power  readings  of  similar  conveyors  installed  at 
other  mines  it  is  expected  that  1  h.p.-hour  will  convey  2|  tons  1  mile.  This 


108  DRIVING  THE  BELT 

is  more  than  twice  the  amount  which,  according  to  the  usual  formulas,  can 
be  carried  over  ordinary  idlers  with  grease  lubrication  in  the  bores  of  the 
pulleys. 

Future  Development  in  Long-distance  Conveying.  —  The  merits  of 
improved  carrying  idlers  are  described  in  Chapter  IV.  Briefly,  they  save 
power,  reduce  the  cost  of  belts  and  require  less  attendance.  These  factors 
are  worth  considering  even  in  small  conveyors,  but  when  large  quantities 
of  material  are  to  be  handled  over  long  distances  they  are  of  the  greatest 
importance.  It  is  reasonable  to  expect  great  improvements  in  the  con- 
struction and  lubrication  of  ball-bearing  and  roller-bearing  idlers;  when 
this  is  brought  about,  and  when  improved  loading  means  are  used,  it  is  prob- 
able that  belts  will  be  run  faster  than  at  present,  possibly  up  to  the  speed 
at  which  fine  material  will  be  blown  off  the  belt  by  the  resistance  of  the  air. 
Belt  conveyors  will  then  be  more  efficient  machines  for  the  transport  of 
large  quantities  of  material  and  can  be  used  economically  for  distances 
which  now  seem  impracticable. 

Relation  of  Horse-power  to  Belt  Tension.  —  Knowing  the  horse-power 
to  drive  a  belt  conveyor,  we  can  find  out  the  tension  in  the  belt.  The 


Pull  in  Entering  Belt 


u          u 

Horae  Power  Pull- 1VT  2 


-  Pull  in  Le»Tlng  Belt 


f 

|  _  | 

FIG.  98.  —  Relation  between  Horse-power  Pull  and  Belt  Tensions. 


Tension  Weight 
or  Equivalent 


h.p.  X33,000 

horse-power  pull,  or  effective  pull,  is -    in   pounds. 

belt  speed  in  ft.  per  min. 

This  is  not  the  actual  or  total  pull  in  the  belt,  because  in  order  to  maintain 
the  belt  in  driving  contact  with  the  driving  pulley  the  belt  must  be  kept 
under  tension  on  both  the  entering  and  the  leaving  sides  of  the  pulley. 
If  in  Fig.  98  we  call  the  pull  on  the  entering  belt  TI  and  the  pull  in  the 
leaving  belt  772,  the  effective  pull  in  the  belt  which  does  useful  work  or  which 
transmits  horse-power  is  TI  —  Tz.  This  gives  a  difference  of  belt  tensions 
but  not  the  tensions  themselves.  From  considerations  of  belt  wrap  and 

T 
belt  friction  we  can  find  the  ratio  of  the  tensions  — ,  and  by  combining  this 

J.  2 

with  TI  —  T»  we  determine  the  actual  values  of  TI  and  TV 

Thickness  of  Belt  as  Determined  by  Belt  Tension. — The  total  tension 
TI  on  the  pulling  side  of  a  belt  is  made  up  of  the  horse-power  pull  plus 
an  added  tension  necessary  to  maintain  a  driving  contact  between  belt 
and  pulley.  The  tension  T2  on  the  leaving  side  should  be  only  what  is 

T 

necessary  to  maintain  the  driving  contact.     The  ratio  —  depends  upon  the 


DETERMINATION  OF  BELT  TENSION 


109 


coefficient  of  friction  between  belt  and  pulley  and  on  the  angle  in  degrees 
of  belt  wrap  on  the  pulley.  »  Calling  the  former  /  and  the  latter  a,  the 
mathematical  expression  is  -, 

(6) 


Experiments  have  shown  that  for  dry,  clean  rubber  belts  on  cast-iron 
pulleys  /  =  .25,  and  when  the  pulleys  are  lagged  or  covered  with  rubber 

T 

/  =  .35.      Table   20   gives   values  of  —  for  these  two  coefficients  and  for 

Tz 

various  angles  of  belt  wrap. 
TABLE    20—  RATIO   OF    ~    FOR   VARIOUS    CONDITIONS    OF    DRIVING 

-t  2 

!Fi  =  Pulling  Tension  at  Drive  Pulley,  772  =  Slack  Tension  at  Drive  Pulley 


Angle  of 
Belt  Wrap, 
Degrees 

Bare  Iron 
Pulleys 

Lagged 
or  Covered 
Pulleys 

Angle  of 
Belt  Wrap, 
Degrees 

Bare  Iron 
Pulleys 

Lagged 
or  Covered 
Pulleys 

135 

1.80 

2.28 

215 

2.56 

3.72 

140 

1.84 

2.35 

220 

2.61 

3.83 

145 

1.88 

2.43 

225 

2.67 

3.95 

150 

1.92 

2.50 

240 

2.85 

4.33 

155 

1.97 

2.58 

255 

3.04 

4.75 

160 

2.01 

2.66 

270 

3.25 

5.20 

165 

2.06 

2.74 

285 

3.47 

5.70 

170 

2.10 

2.83 

300 

3.70 

6.25 

175 

2.15 

2.91 

315 

3.95 

6.85 

180 

2.19 

3.00 

330 

4.22 

7.51 

185 

2.24 

3.10 

345 

4.51 

8.23 

190 

2.29 

3.19 

360 

4.80 

9.02 

195 

2.34 

3.29 

420 

6.25 

13.00 

200 

2.39 

3.39 

500 

8.86 

21.21 

205 

2.45 

3.50 

600 

13.71 

39.06 

210 

2.50 

3.61 

700 

21.21 

71.96 

Since  the  torsion  at  the  drive  shaft  is  measured  by  the  horse-power  pull 

T 
which  is  Tt  —  To.  and  since  the  total  pull  in  the  belt  is  TV  the  ratio — 

1  1  —  -/  2 

expresses  the  relation  between  the  actual  effective  horse-power  pull  and  the 
total  pull  in  the  belt.  These  ratios  are  given  in  Table  21. 

From  Table  20  we  see  that  for  a  simple  drive  with  180°  wrap  on  an 

T 

iron  pulley  —  =2.193  or  T2  =  .456Ti;  then  since  horse-power  pull  =  Ti-T3 
T-i 

horse-power  pull  =. 544  Ti  or  Ti  =1.838  horse-pull  (see  Table  21).  That 
is,  the  total  tension  in  the  pulling  side  is  over  1.8  times  what  is  necessary 
to  move  the  load  and  overcome  idler  friction. 

If  the  pulley  is  lagged,  the  ratio  falls  to  1.5,  and  if  by  use  of  a  snub 
pulley  the  wrap  on  the  lagged  pulley  is  increased  to  240°,  the  total  tension 
i  See  Kent's  M.  E.  Pocketbook. 


110 


DRIVING  THE  BELT 


Ti  becomes  only  1.3  times  the  horse-power  pull  on  effective  tension.     (See 
Table  21.) 


TABLE  21.— RATIO  OF 


FOR  VARIOUS    CONDITIONS   OF    DRIVING 


=  Tension  in  Pulling  Belt  at  Drive  Pulley,  T2  =  Tension  in  Slack  Belt  at  Drive  Pulley, 
TI  —  Tz  =  Horse-power  Pull 


Angle  of 
Belt  Wrap, 
Degrees 

Bare  Iron 
Pulleys 

Lagged 
or  Covered 
Pulleys 

Angle  of 
Belt  Wrap, 
Degrees 

Bare  Iron 
Pulleys 

Lagged 
or  Covered 
Pulleys 

135 

2.25 

1.78 

215 

1.64 

1.37 

140 

2.19 

1.74 

220 

1.62 

1.35 

145 

2.14 

1.70 

225 

1.60 

1.34 

150 

2.08 

1.67 

240 

1.54 

1.30 

155 

2.03 

1.63 

255 

1.49 

1.27 

160 

.99 

1.60 

270 

1.45 

1.24 

165 

.95 

1.57 

285 

1.41 

1.21 

170 

.91 

1.55 

300 

1.37 

1.19 

175 

.87 

1.52 

315 

1.34 

1.17 

180 

.84 

1.50 

330 

1.31 

1.15 

185 

.81 

1.48 

345 

1.29 

1.14 

190 

.78 

1.46 

360 

1.26 

1.13 

*      195 

.75 

1.44 

420 

1.19 

1.08 

200 

.72 

1.42 

500 

1.13 

1.05 

205 

.69 

1.40 

600 

1.08 

1.03 

210 

.67 

1.38 

700 

1.05 

1.01 

If  the  belt  is  wrapped  around  two  driving  pulleys  as  in  the  tandem- 
geared  drive  (Fig.  102,  p.  121)  the  total  angle  of  wrap  may  be  greater  than 

T 
360°,  the  ratio  — -  increases   (see  Table  20)   and  the  ratio  of   7\  to  the 

T2 

horse-power  pull  decreases  toward  1 ;  when  that  point  is  reached,  all  of  the 
strength  of  the  belt  is  effective  for  moving  the  load  and  overcoming  idler 
friction.  Practically,  the  ratio  never  reaches  unity,  but  for  a  wrap  of 
420°,  the  total  tension  is  only  8  per  cent  more  than  the  effective  horse-power 
tension  (see  Table  21);  this  means  that  a  belt  for  such  a  case  need 
hardly  be  thicker  than  is  required  to  transmit  the  horse-power  pull,  but 
while  for  a  plain  180°  wrap  a  4-ply  belt,  for  instance,  might  transmit  the 
horse-power  pull,  it  would  take  4x1.8  (see  above)  =7.2  plies  to  give  the 
added  strength  necessary  to  maintain  the  driving  contact  between  the 
belt  and  the  pulley. 

Calculation  of  Number  of  Plies. — The  first  step  is  to  determine  the  horse- 
power of  the  conveyor  from  formula  (4)  on  page  98  or  from  formula  (5), 
page  106,  or  from  Tables  17,  18,  19,  then  the  horse-power  pull  from  horse- 
h.p.X  33,000 


power  pull 


8 


where  S  is  belt  speed  in  feet  per  minute.      This 


horse-power  pull  multiplied  by  the  factor  from  Table  21  gives  the  neces- 
sary stress  TI  on  the  pulling  side  of  the  belt. 


ULTIMATE  STRENGTH  AND  WORKING  TENSION  111 

Belts  are  said  to  be  worth  so  many  pounds  per  ply  per  inch  of  width, 
calling  this  figure  p,  and  the  nu'mber  of  plies  n,  and  the  width  of  belt  W, 

Tl  * 

then  n  = . 

pW 

Ultimate  Strength  and  Working  Tension. — Haddock's  experiments  with 
a  12-inch  4-ply  conveyor  belt  (Transactions,  A.  S.  M.  E.,  Vol.  30,  1908) 
showed  a  stretch  which  was  not  considered  excessive  under  1500-pound 
belt  tension  or  31  pounds  per  inch  per  ply.  When  the  load  was  increased 
to  42  pounds  per  inch  per  ply  the  belt  in  its  total  length  of  158  feet  stretched 
3  feet  more  than  under  the  31-pound  tension.  When  the  load  was  increased 
to  62  pounds  per  inch  per  ply  there  was  a  further  stretch  of  8  inches  which 
did  not  increase  after  30  minutes  run  under  that  load. 

The  proper  working  tension  is  determined  first  by  the  stretch,  and, 
second,  by  the  necessity  of  avoiding  pulls  too  high  for  the  metal  fasteners 
generally  used  to  join  the  ends  of  belts.  (For  fastenings,  see  Chapter  III.) 
Baldwin  in  Marks'  M.  E.  Handbook,  1st  ed.,  p.  1179,  gives  18.4  pounds  per 
inch  per  ply  as  the  proper  tension;  the  line  diagrams  published  by  Robins 
are  based  on  that  same  value;  Stephens- Adamson  recommend  20  pounds 
except  for  temporary  work;  Goodyear  uses  factors  based  on  27.5  pounds 
for  belts  made  of  36-ounce  duck,  25.2  pounds  for  32-ounce  duck  and  23. 
pounds  for  28-ounce  duck;  Goodrich  uses  24  pounds  for  32-ounce  or  28 
ounce  duck;  Jeffrey  uses  tables  based  on  30  pounds;  Main  Belting  Co. 
uses  30  pounds  for  32-ounce  canvas  belt  duck  (see  p.  46). 

There  is  no  notable  difference  in  the  ducks  used  in  the  rubber  belts  made 
or  sold  by  these  various  concerns;  the  differences  in  the  allowed  working 
tensions  merely  represent  differences  of  opinion  as  to  what  is  proper  and 
safe.  It  is  true,  however,  that  there  is  a  growing  tendency  toward  the  use 
of  higher  unit  stresses  than  were  common  five  or  ten  years  ago. 

Ultimate  Strength  of  Belts. — These  values  are  based,  of  course,  on  the 
ultimate  strength  of  the  belt.  It  has  been  the  practice  to  say  that  ordinary 
conveyor  belts  would  show  an  ultimate  strength  of  360  pounds  per  inch  per 
ply;  but  since  belts  vary  as  to  weight  of  duck  it  is  better  to  say  that  the 
following  represents  an  average  for  belts  of  American  make  when  tested  in 
the  whole  width:  28-ounce,  300  pounds;  30-  and  32-ounce,  325  pounds; 
36-ounce,  360  pounds.  It  is  not  usually  possible  to  get  these  results  from 
test  strips  1  or  2  inches  wide  for  the  reasons  given  on  page  39 ;  such  tests, 
as  well  as  those  of  strips  of  duck  either  before  or  after  making  up  into 
belt,  may  show  considerable  variation  depending  on  the  different  methods 
of  testing  employed  by  manufacturers.  On  this  point,  see  page  33.  The 
weight  of  duck  is  in  itself  no  sure  indication  of  the  strength  of  the  belt; 
the  degree  of  twist  in  the  threads,  and  the  number  of  threads  in  warp  and 
filler,  the  method  of  vulcanization — all  of  these  have  their  influence;  but 
as  a  basis  for  estimating  'working  strengths,  the  values  given  may  be  taken 
as  representing  average  belt  manufacture. 

Working  Tension  of  Belts. — In  choosing  the  working  tension  it  is  well 
to  be  guided  by  the  conditions  under  which  the  belt  is  to  be  used.  If  it 


112 


DRIVING  THE  BELT 


forms  part  of  a  permanent  installation,  has  a  cover  thick  enough  for  protec- 
tion, and  seems  no  more  likely  to  fail  from  cutting  and  abrasion  than  from 
separation  of  plies  or  loss  of  "  life  "  in  the  friction,  then  for  long  service  the 
unit  stress  should  be  under  25  pounds;  but  for  a  temporary  job,  or  where 
the  life  of  the  belt  is  likely  to  be  terminated  by  an  accident  or  by  the  loss 
of  its  cover,  then  the  unit  stress  can  be  made  higher  than  25  pounds  and  up 
to  30  pounds. 

For  a  practical  example,  where  the  belt  tension  was  made  higher  than 
25  pounds,  see  p.  117. 

Faulty  Methods. — In  some  line  diagrams  published  to  show  proper 
belt  thickness  and  in  the  usual  formulas  the  unit  belt  stresses  are  not  stated, 
but  are  included  in  factors  or  "  constants  "  which  vary  according  to  the 
nature  of  the  drive,  the  effect  being  to  make  the  allowable  unit  stress  high 
for  the  lagged  drive  with  a  large  angle  of  wrap  and  low  for  the  drive  with  a 
plain  iron  pulley  with  a  wrap  of  180°  or  thereabouts.  These  methods  do 
not  show  any  relation  between  the  strength  of  the  belt  and  the  tension 
under  which  it  is  worked;  it  seems  much  better  to  start  with  a  definite 
unit  stress  per  inch  per  ply  and  fix  the  belt  thickness  after  the  total  belt 
stress  has  been  determined.  This  is  the  purpose  of  Table  20  and  Table 
21.  From  these  the  actual  belt  stresses  Ti  and  T2  can  be  calculated  and 
from  them  we  can  find  the  size  of  the  drive  shaft,  the  strength  of  the  machin- 
ery supports  and  other  details  in  the  design  of  a  belt  conveyor.  In  the  other 
methods  referred  to  the  true  values  of  Ti  and  T-2  are  masked  in  the  calcula- 
tions and  cannot  readily  be  determined. 

A  formula  published  in  1908  (Trans.,  A.  S.  M.  E.,  Vol.  30)  and  still 
retained  in  a  few  publications  gives 

h.p.  X33,000 
~SB~ 

where    X  =  stress  in  the  belt  in  pounds  per  inch  of  width; 
S  =belt  speed  in  feet  per  minute; 
B  —  width  of  belt  in  inches. 


This  is  wrong  because  it  ignores  the  difference  between  horse-power  pull 

and  Ti  (see  p.  109).  For  a  simple 
drive  with  180°  wrap  it  gives  values 
too  low  by  45  per  cent. 

Tension  in  Belts  due  to  Incline 
of  Conveyor. — In  an  inclined  belt 
conveyor,  if  W  (Fig.  99)  is  the 
weight  of  the  belt  on  each  run,  and 
A  in  the  angle  of  incline  from  the 

FIG.  99.-Belt  Tension  Due  to  Angle  of        horizontal,      the    component    of    W 
Incline.  parallel  to  the  incline  directed  down- 

ward is  W  sin  A  and  the  direct  load  on  the   idlers   is   W  cos   A.     The 


WIDTH  OF  BELTS 


113 


resistance  of  the  latter  to  turning"  is  W  cos  Af—  or  about  .07  W  cos  A  with 

grease  lubrication,  and  -therefore  the  tendency  of  the  belt  to  run  down- 
hill or  produce  an  added  tension  at  the  head  is  W(sin  A  — .07  cos  A). 

When  A  =  4°,  sin  A  is  nearly  equal  to  .07  cos  A,  and  the  expression 
becomes  zero,  that  is,  on  angles  less  than  4°  there  is  no  tendency  of  the 
unloaded  belt  to  run  downhill  and  hence  no  belt  tension  at  the  head  due  to 
the  angle  of  incline  and  the  weight  of  the  belt. 

Table  22  gives  values  of  (sin  A— .07  cos  A)  for  various  slopes.  Thus, 
on  a  20°  incline  400  feet  long  with  grease-lubricated  idlers  the  pull  in  a 
belt  weighing  10  pounds  per  linear  foot  is  400x10  X. 28  =  1120  pounds. 
Since  this  is  exerted  on  each  run  of  belt,  the  total  pull  due  to  the  weight 
of  the  belt  which  produces  bending  in  the  head  shaft  is  2240  pounds. 


TABLE  22.— PULL  IN  CONVEYOR  BELT  AT  HEAD  PULLEY 
DUE  TO  ANGLE  OF  SLOPE 


Angle     of     incline     A  — 
Degrees  

2° 

4° 

6° 

8° 

10° 

12° 

14° 

10° 

18° 

20° 

22° 

24° 

26° 

Percentage  of  Weight  of  Belt 


Grease  lubricated  idlers.  .  . 

0 

0 

3 

7 

10 

14 

17 

21 

24 

28 

31 

34 

37 

Ball  bearing  or  roller  bear- 
ing Idlers  .  .           

0 

4 

7 

11 

14 

17 

21 

24 

28 

31 

34 

38 

41 

When  ball-bearing  or  roller-bearing  idlers  are  used  the  coefficient  of 
idler  friction  may  be  as  low  as  .03;  then  at  all  angles  over  2°  there  is  a 
tension  in  the  belt  due  to  the  incline  which  increases  to  greater  percentages 
of  the  weight  at  the  angles  of  incline  ordinarily  used.  These  are  given  in 
the  last  line  of  the  table. 

Width  of  Belts. — The  width  of  a  belt  depends,  first,  on  the  size  of  the 
pieces  handled,  and,  second,  on  the  capacity  required.  So  far  as  capacity 
is  concerned,  the  width  can  be  determined  from  the  speed  and  from  Table 
26,  but  the  more  important  requirement  is  that  the  belt  shall  be  wide  enough 
for  the  largest  pieces.  This  is  really  based  on  the  necessity  of  having  a 
loading  chute  that  will  not  choke.  A  chute,  to  avoid  spilling  off  the  belt, 
can  hardly  be  wider  than  §  TP  (W  =  width  of  belt),  and  since  the  width  of  a 
chute  to  avoid  choking  must  be  at  least  three  times  the  size  of  the  pieces 
when  they  are  uniform  in  size,  it  follows  that  the  belt  width  should  be 
about  five  times  the  size  of  the  pieces  where  they  are  all  of  one  size,  as  in 
sized  anthracite  coal  and  other  screened  materials  (see  Table  23,  column 
A).  But  run-of-mine  coal,  crushed  rock  and  such  material  handled  on 
belt  conveyors  seldom  consists  of  pieces  of  uniform  size.  For  these,  the 
width  of  the  chute  can  be  about  twice  the  size  of  the  largest  pieces  with  a 


114 


DRIVING  THE  BELT 


fair  chance  that  no  two  of  them  will  lock  in  position  to  block  the  flow. 
Under  those  conditions  the  ratio  of  belt  width  to  the  size  of  the  occasional 
large  lump  can  be  according  to  column  B  of  Table  23. 

TABLE  23.— WIDTH  OF  BELT  ACCORDING  TO  SIZE  OF  MATERIAL 


Width  of 
Belt,  Inches 

A 
Size,  Inches 

B 

Size,  Inches 

Width  of 
Belt,  Inches 

A 
Size,  Inches 

B 

Size,  Inches 

12 

ii 

2 

32 

6| 

12 

14 

2 

3 

34 

7 

13 

16 

2| 

4 

36 

n 

14 

18 

3 

5 

38 

^ 

15 

20 

3£ 

6 

40 

8 

16 

22 

4 

7 

42 

8* 

17 

24 

4* 

8 

44 

9 

18 

26 

5 

9 

48 

10 

20 

28 

6| 

10 

54 

11 

22 

30 

6 

11 

60 

12 

24 

NOTE. — If  the  material  is  uniform  in  size  use  Column  A. 

Column  B  shows  the  size  of  lumps  which  may  safely  be  carried  if  those  lumps  do  not 
exceed  20  per  cent  of  the  mass,  and  the  remainder  is  mostly  small. 

Thickness  of  Belt  as  Determined  by  Troughing. — When  belts  are  too 
stiff  to  conform  when  empty  to  the  contour  of  the  troughing  idlers  they 
lose  the  guiding  effect  of  the  horizontal  pulleys  and  are  likely  to  be  deflected 
from  a  straight  course  by  the  steering  action  of  the  inclined  pulleys  (see 
p.  79).  This  effect  of  the  inclined  pulleys  depends  upon  the  angle  of  their 
inclination;  it  was  very  noticeable  with  45°  and  35°  troughing  angles 
and  it  led  to  the  use  of  the  stepped-ply  belt  (see  p.  16).  More  recently 
it  prompted  the  general  adoption  of  angles  of  30°  or  less,  and  in  current 
practice  it  limits  the  thickness  of  belts  to  what  will  conform  to  the  contour 
of  three-pulley  idlers  troughed  30°  or  less  or  five-pulley  idlers  with  angles 
of  15°  and  30°.  Excessive  thickness  leads  to  the  use  of  side-guide  idlers 
at  short  intervals,  skewed  idlers,  tilted  idlers,  all  expendients  to  overcome 
the  natural  tendency  of  troughing  idlers  to  "  steer  "  a  belt  (see  p.  79). 

On  the  other  hand,  if  belts  are  too  thin  they  deflect  too  much  under 
load;  they  are  more  likely  to  be  pinched  in  the  "wedge  angle  "  between 
idler  pulleys  (see  Fig.  36,  p.  15);  and  if  side-guide  idlers  are  used,  the  edge 
of  the  belt  may  be  turned  back  or  folded  over  by  pressing  against  them. 
Moreover,  the  belt  may  crack  longitudinally  from  a  lack  of  enough  filler 
threads  to  withstand  the  repeated  bending  back  and  forth  over  troughing 
idlers. 

Based  upon  these  considerations,  Table  24  has  been  prepared  to  show 
the  maximum  and  minimum  number  of  plies  for  different  widths  of  rubber 
belt.  The  values  given  are  a  composite  between  those  given  by  several 
authorities;  those  for  belts  wider  than  30  inches  lean  toward  plies  heavier 
than  it  was  once  thought  proper  to  use;  but  since  those  sizes  are  generally 
run  on  five-pulley  idlers  it  is  not  necessary  to  limit  them  to  those  thicknesses 


DESIGN  OF  BELT  CONVEYORS 


115 


that  will  bend  sharply.  The  natural  bend  of  the  heavy  belts  shown  in  Figs. 
76  and  77  is  much  more  pronounced  than  is  necessary  to  fit  any  five-pulley 
standard  idler.  Fifty-four-inch  Jfrelts  with  11  plies  and  60-inch  belts  with 
12  plies  of  extra  heavy  duck  are  in  successful  use  in  five-pulley  idlers. 

TABLE  24.— MAXIMUM    AND    MINIMUM    THICKNESS   OF   RUBBER    BELT 
FOR  PROPER  TROUGHING  AND  LOADING  ON  STANDARD  IDLERS 


Width  of 
Belt,  Inches 

Maximum 
Plies 

Minimum 
Plies 

Width  of 
Belt,  Inches 

Maximum 
Plies 

Minimum 
Plies 

12 

4 

3 

32 

8 

5 

14 

4 

3 

34 

8 

5 

16 

5 

4 

36 

9 

5 

18 

5 

4 

38 

9 

6 

20 

6 

4 

40 

9 

6 

22 

6 

4 

42 

10 

6 

24 

7 

5 

44 

10 

6 

26 

7 

5 

48 

11 

7 

28 

8 

5 

54 

11 

7 

30 

8 

5 

60 

12 

8 

When  belts  are  run  flat  or  on  flared  idlers  or  on  three-pulley  idlers 
troughed  20°  or  less,  the  maximum  thickness  of  belt  is  not  limited  to  the 
plies  given  in  Table  24,  so  far  as  troughing  is  concerned.  Such  idlers 
come  nearer  to  matching  the  natural  free  bend  of  belts  24  inches  and  nar- 
rower than  do  five-pulley  idlers  and  most  commercial  three-pulley  idlers. 
(See  Fig.  78.)  For  that  reason  they  are  better  suited  to  thick  rubber  belts 
and  especially  to  canvas  belts  and  balata  belts,  which  are  naturally  stiffer 
than  rubber  belts. 

For  thickness  of  belt  as  determined  by  the  tension,  see  page  110. 

Design  of  Belt  Conveyors. — The  successive  steps  in  the  design  of  a  belt 
conveyor  may  be  set  down  thus : 

Refer  to 

1.  From  known  size  of  material  select  width  of  belt p.  114 

2.  If  conveyor  is  inclined,  assume  a  safe  angle p.  142 

3.  Choose  proper  speed  of  belt  according  to  nature  of  material, 

size   of  lumps,   angle  of  incline,   length  of  belt CHAP.  VII 

4.  From  3  and  from  capacity  required  determine  belt  width .  .  TABLE  26 

5.  Use  1  or  4,  whichever  is  the  larger 

6.  Consider  what  kind  of  supporting  idlers  are  to  be  used ....  CHAP.  IV 

7.  From  6  calculate  horse-power  for    belt,  and  load,  not  in- 

cluding transmission  losses.     If  conveyor  is  inclined  or  has 

a  tripper  add  for  that CHAP.  V 

8.  From  7  and  3  calculate  horse-power  pull  and  from  that  the 

belt  tension TABLE  21 

9.  Assume  a  unit  stress  per  inch  per  ply  and  from  8  determine 

the  number  of  plies p.  110 

10.  If  the  belt  is  too  thick  in  proportion  to  its  width,  figure  on  a 
more  efficient  drive,  or  use  a  higher  unit  stress,  or  shallower 
troughing,  or  else  use  a  wider  belt p.  114 


116  DRIVING  THE  BELT 

Refer  to 

11.  Determine  diameters  of  pulleys  drive,foot,  bend,  snub  or  tripper  p.  127 

12.  Lay  out  gearing  to  suit  source  of  power 

13.  From  7  and  12,  determine  horse-power  to  drive  by  adding 

for  losses  in   power   transmission p.  98 

14.  Calculate  drive  shaft  for  torsion  and  bending,  other  shafts 

for  bending  only 

15.  Consider  kind  of  belt  and,  if  rubber,  thickness  of  cover. .  . .  CHAP.  Ill 

16.  Consider  design  of  loading  chute  and  skirt-boards CHAP.  VII 

17.  Consider  design  of  discharge  chute CHAP.  VIII 

18.  Consider  location  and  style  of  take-ups CHAP.  VI 

19.  Consider  protective  deck,  cleaning  brush,  location  of  return  CHAP.  IX 

idlers,  use  of  tripper CHAP.  VIII 

Errors  or  mistakes  of  judgment  in  the  design  of  belt  conveyors  are  not 
all  equally  serious.  Some  cause  the  belt  to  wear  out  sooner,  and  others 
can  be  corrected  after  the  conveyor  is  in  service.  But  there  are  two  which 
are  very  serious;  they  cannot  be  corrected  except  after  aggravating  delay 
and  much  expense  and  often  by  humiliating  makeshifts.  These  are  a  belt 
too  narrow  for  the  size  of  the  material  or  the  "  peak  "  capacity,  and  an 
inclined  belt  too  steep.  Designers  should  be  very  careful  on  these  points 
(see  p.  148). 

Design  of  a  Specimen  Belt  Conveyor. — It  was  required  to  carry  2000 
tons  of  limestone  in  ten  hours  from  a  crusher  to  a  loading  chute,  length, 
223  feet  on  18°  incline;  height  of  lift,  69  feet.  The  crushed  material  weighed 
100  pounds  per  cubic  foot  and  ranged  in  size  from  5  to  16  inches;  average 
about  8  inches.  The  crusher  was  rated  at  250  tons  an  hour,  but  it  was 
fed  rather  intermittently  from  dump  cars,  and  it  could  deliver  at  a  higher 
rate  for  a  few  minutes  when  the  rock  did  not  require  much  reduction  in 
size.  It  was  decided  to  provide  for  an  excess  of  one-third,  or  an  hourly 
rate  of  333  tons,  equivalent  to  6660  cubic  feet  per  hour.  A  30-inch  belt 
would  give  that  capacity  at  a  comparatively  slow  speed  (see  Table  26), 
but  on  account  of  the  16-inch  lumps  it  was  necessary  to  use  a  40-inch  belt 
(see  Table  23).  This  is  usually  rated  at  5120  cubic  feet  per  hour  at  100 
feet  per  minute  (see  Table  26),  but  since  the  conditions  for  loading  the 
belt  under  the  crusher  were  not  favorable  for  a  uniform  feed  it  was  taken  at 
4500  cubic  feet.  The  belt  speed  for  the  capacity  required  was  under  150 
feet  per  minute,  but  after  some  consideration  of  motor  speeds  and  room 
available  for  gearing  it  was  decided  to  run  the  belt  225  feet  per  minute,  but 
with  a  loading  lighter  than  usual  so  as  not  to  exceed  333  tons  an  hour 
capacity. 

The  next  step  was  to  determine  the  horse-power  for  the  belt. 
From  Table  17  the  h.p.  to  run  the  conveyor  empty  is  2.68x2.25=   6.00 
From  Table  18  the  h.p.  to  carry  333  tons  over  223-foot  level  =5.25 

From  Table  19  the  h.p.  to  lift  333  tons  69  feet  vertically  =23.20 


or  a  total  of  34.5  h.p.  34 . 45 


.  HOW  NOT  TO  DO  IT  117 

34  5  X33  000 

The  belt  pull  Ti  —  Tz  corresppnUing  to  this  is  — =  5060  pounds. 

ZZo 

To  determine  the  tQital  tensi&i   Tl  in  the  belt  refer  to  Table  21. 

If  we  use  a  180°  wrap  on  a  lagged  pulley  Ti  =  5060  X  1.50  =  7590  (No.  1) 
If  we  use  a  240°  wrap  with  a  snub  pulley  Tl  =  5060  X  1.30  =  6578  (No.  2) 
If  we  use  a  420°  wrap  with  tandem  pulleys  Ti  =  5060  X  1.08  =  5464  (No.  3) 

Rubber  belts  are  rated  anywhere  from  18  to  30  pounds  permissible  ten- 
sion per  inch  per  ply  (see  p.  111).  Taking  24  pounds,  a  40-inch  belt  is 
worth  960  pounds  per  ply.  On  this  basis,  the  first  drive  would  take  8  plies; 
the  second,  7;  the  third,  6  plies.  We  now  make  an  assumption  to  get  from 
Table  22  the  pull  due  to  the  incline  of  the  belt.  A  40-inch  8-ply  belt  with 
|-inch  cover  weighs  about  12.5  pounds  per  foot;  the  added  tension  for  the 
18°  incline  is  12.5  X223X.24  =669  pounds.  Adding  this,  we  get  for  the 
three  cases  8259  pounds,  7247  pounds  and  6133  pounds,  for  the  total  tension 
in  the  pulling  side  of  the  belt. 

Of  the  3  alternative  drives,  No.  1  requires  more  than  8  plies  to  keep  the 
unit  tension  below  24  pounds ;  No.  2  would  stress  an  8-ply  belt  less  than  23 
pounds;  while  No.  3  would  put  only  22  pounds  unit  tension  in  a  7-ply  belt 
with  some  saving  in  the  cost  of  the  belt. 

It  was  decided  to  adopt  No.  1,  the  drive  with  a  half  wrap  on  a  lagged 
pulley  and  stress  the  belt  to  26  pounds  per  inch  per  ply  of  32-ounce  duck. 
There  were  several  reasons:  it  required  less  machinery  at  the  head,  and 
lighter  supports;  there  would  be  no  reverse  bend  in  the  belt  and  particles 
of  stone  would  not  be  ground  into  the  cover  as  would  be  the  case  if  a  snub 
pulley  or  a  tandem-geared  drive  were  used. 

Sometimes  a  unit  stress  of  26  pounds  would  be  open  to  objection,  but 
in  this  case  it  was  thought  that  the  life  of  the  belt  would  be  fixed  by  the 
ability  of  the  cover  to  withstand  cutting  and  abrasion,  and  that  a  unit 
stress-  of  26  pounds  might  represent  a  proper  balance  for  the  life  of  the 
body  of  the  belt  considering  the  weight  of  the  duck.  The  belt  was  installed 
with  a  60-inch  rubber-covered  head  pulley;  it  ran  three  years  and  handled 
a  little  over  2,000,000  tons  of  stone,  a  very  satisfactory  performance  and 
quite  remarkable,  since  the  f-inch  cover  was  rather  light  for  the  large  pieces 
carried  on  the  belt.  The  foot  pulley  was  42  inches  in  diameter,  over  5 
inches  for  every  ply  of  belt,  and  the  diameter  of  the  head  pulley  was  7£ 
inches  for  each  ply.  The  good  service  of  the  belt  may  be  credited  in  part 
to  these  large  pulleys  and  to  the  fact  that  there  were  no  reverse  bends. 

How  Not  to  Do  It. — The  belt  just  referred  to  may  be  contrasted  with 
another  doing  similar  work  in  a  different  part  of  the  country:  a  large  rock 
crusher,  fed  by  side-dump  cars,  delivered  to  a  36-inch  belt  inclined  between 
20°  and  21°,  250-foot  centers  and  run  at  350  feet  per  minute.  There  was 
no  feeder  over  the  crusher  nor  between  it  and  the  belt.  Some  of  the  product 
was  required  to  be  in  large  pieces  with  least  dimension  about  8  inches, 
hence  the  crusher  was  set  to  produce  that  size.  When  the  cars  were  dumped 


118  DRIVING  THE  BELT 

the  smaller  stuff  rushed  through  the  crusher  and  on  to  the  belt.  On  account 
of  the  high  speed,  350  feet  per  minute,  and  the  steep  angle,  the  pick-up  was 
bad,  the  rock  did  not  acquire  belt  speed  promptly  and  the  sharp  corners 
cut  and  tore  the  belt.  Once  started  up  the  incline,  pieces  of  rock  would 
roll  back  and  jump  off  the  belt.  To  prevent  that,  continuous  skirt-boards 
were  then  added  for  the  length  of  the  incline,  and  finally  to  prevent  the  tail 
end  of  a  load  on  the  belt  from  sliding  or  rolling  back,  sets  of  pawls  or  stops 
were  placed  over  the  belt  every  20  or  30  feet.  Each  set  consisted  of  eight 
3-by-|-mch  steel  bars  set  edgewise,  pivoted  about  3  feet  above  the  belt 
and  mounted  so  that  the  lower  ends  of  the  bars  could  yield  or  move  upward 
with  the  travel  of  rock  up  the  incline  but  be  rigid  in  -the  opposite  direction 
to  prevent  any  downward  movement.  Then  a  reciprocating  plate  feeder 
driven  from  the  foot  shaft  was  interposed  between  the  crusher  and  the  belt. 
When  this  installation  was  inspected  it  had  been  in  service  about  six  months, 
the  cover  of  the  belt  showed  signs  of  severe  cutting  and  scraping,  several 
sections  had  been  cut  out  and  replaced  by  new  belt  and  belt  fasteners  were 
used  to  hold  the  belt  together  where  it  had  been  split  lengthwise.  The 
belt  had  been  a  good  one,  apparently  6-ply  with  a  cover  at  least  |-inch  thick. 

The  angle  of  incline  in  this  case  should  have  been  17°  or  less  and  the 
speed  of  the  belt  (see  Table  30,  p.  154)  not  over  200  feet  per  minute. 
This  would  have  provided  a  capacity  far  in  excess  of  the  1000  tons  per 
day  required  and,  with  a  feeder,  would  have  allowed  for  some  irregularity 
in  the  feed  to  the  crusher  without  reducing  the  tonnage  per  hour. 

Where  to  Drive. — The  best  place  for  a  single-pulley  drive  is  at  the  head 
or  delivery  end,  because  when  the  drive  is  placed  there  all  of  the  loaded 
side  is  under  tension,  and  it  is  less  likely  to  run  crooked  than  if  it  were 
partly  slack.  One  way  to  make  a  belt  run  straight  over  troughing  idlers 
is  to  pull  it  very  tight  (see  p.  81);  hence  in  conveyors  driven  at  the  foot 
there  is  a  possibility  that  when  the  belt  runs  off  to  one  side  the  attendant 
may  help  to  straighten  it  by  loading  or  adjusting  the  take-ups  and  thus 
put  a  stress  in  the  belt  far  in  excess  of  what  is  necessary  for  carrying  the 
load  or  for  maintaining  belt  contact  on  the  driving  pulley. 

Driving  at  the  Foot. — When  an  inclined  belt  is  driven  at  the  foot,  the 
pulley  contact  there  is  reduced  by  the  tendency  of  the  belt  to  run  downhill 
and  form  slack  at  the  bottom.  The  force  which  acts  in  this  way  is  on  grease- 
lubricated  idlers,  TF(sin  A  —  .07  cos  A)  (see  p.  113).  For  a  slope  of  20° 
this  amounts  to  28  per  cent  of  the  weight  of  the  belt  on  the  up-run  or  on 
,the  down-run;  hence,  to  maintain  the  proper  relation  between  horse-power 
pull,  TI  and  TI  (see  p.  110)  the  belt  tension  at  the  foot  pulley  must  be 
increased  by  that  amount  by  adjusting  or  loading  the  take-ups.  The 
maximum  belt  tension  in  such  a  case  is  at  the  head,  where  it  exceeds  the 
tension  at  the  foot  by  W(s'm  A  —.07  cos  A}. 

Another  difficulty  with  driving  at  the  foot  pulley  is  the  disposal  of  the 
slack  belt  as  it  leaves  the  pulley.  Usually  the  loading  point  is  too  close  to 
the  foot  to  allow  any  free  hang  of  slack  belt  leading  from  the  foot  pulley. 
The  take-up  cannot  engage  the  belt  on  the  upper  or  loaded  side;  it  is  often 


TANDEM  DRIVES  119 

inconvenient  to  place  it  at  the  head  because  the  discharge  chute  is  there, 
and  the  alternative  is  to  put  it*  oh  the  under  side  near  the  foot  and  let  it 
take  the  belt  under  full  tension.  £ 

When  a  belt  conveyor  is  driven  at  the  foot  instead  of  the  head,  the  pull 
on  the  head  shaft  and  its  bearings  will  be  increased  from  (27i  +  7T2)  to  2Ti. 
In  spite  of  this  and  other  drawbacks  it  is  often  advisable  to  drive  the  con- 
veyor at  the  foot  and  then  take  care  to  keep  the  belt  at  the  proper  tension. 
Such  cases  are  tailings  stackers  and  similar  conveyors  where  it  is  inconven- 
ient to  transmit  power  to  the  head  shaft. 

A  Faulty  Drive. — Fig.  110,  page  129,  shows  a  36-inch  coke  conveyor 
driven  at  the  foot  pulley  B  with  the  take-up  at  D.  The  belt  therefore 
made  three  half  turns  under  full  tension  at  (7,  D,  A,  and  a  bend  at  E. 
With  the  same  general  arrangement  of  pulleys,  the  conveyor  might  have 
been  driven  at  D  with  the  take-up  at  C  or  B.  In  this  case  the  belt  would 
have  made  only  one-half  turn  under  full  tension  at  A  besides  the  bend  at  E, 
there  would  have  been  less  loss  in  journal  friction  and  less  wear  on  the 
belt,  both  internally  and  externally. 

Multiple  Pulley  Drives. — From  Table  21  it  is  apparent  that  the  ability 
of  a  pulley  to  drive  a  belt  increases  rapidly  when  the  angle  of  wrap  exceeds 
240°.  It  is  seldom  possible  to  get  more  than  200°  on  a  plain  pulley  drive 
or  more  than  255°  by  using  a  snub  pulley,  but  by  using  a  second  drive 
pulley  engaging  a  reverse  bend  in  the  belt  the  combined  angle  of  wrap 
may  be  made  360°  or  even  more. 


Foot  Pulley 
with  Take-up 


•2 

FIG.   100. — Belt  Tensions  in  a  Tandem-Pulley  Drive. 

Tandem  Drives. — The  action  of  tandem-pulley  drive  is  shown  in  Fig.  100. 
If  the  pulleys  A  and  B  are  of  the  same  size  and  revolve  at  the  same  speed, 
the  wrap  on  A  being  180°  and  on  B  240°,  the  following  ratios  exist  when 

T  T 

the    pulleys    are    lagged    with    rubber:     —=3.00,    —=4.33.     Therefore 

Tx  TI 

Ti  =3.00x4.33 T2  =  13.00 T7,  (see  Table  20).  That  is,  for  a  comparatively 
low  tension  T2  in  the  leaving  belt  it  is  possible  to  get  a  high  driving  tension 
TI  in  the  entering  belt  and  a  high  horse-power  pull. 


120  DRIVING  THE  BELT 

Comparison  with  Other  Drives. — A  single-pulley  drive  with  180°  wrap 
on  a  lagged  pulley  requires  a  maximum  tension  Ti  of  1500  pounds  for  every 
1000  pounds  of  effective  horse-power  pull;  a  snub  drive  with  240°  wrap 
requires  T\  to  be  1300  pounds,  but  in  a  tandem  drive  with  a  combined 
wrap  of  420°  on  lagged  pulleys  T\  is  only  1080  pounds  for  the  same  effective 
pull  of  1000  pounds.  In  most  tandem  drives  the  combined  angle  of  wrap 
hardly  exceeds  360°,  for  which  7\  would  be  1130  pounds  (see  Table  21) 
for  1000  pounds  effective  horse-power  pull.  In  general,  a  tandem  drive 
will  do  with  a  given  belt  what  requires  a  thicker  and  more  costly  belt  on  a 
single  drive  or  a  snub  drive,  or,  stated  differently,  the  tandem  drive  requires 
only  a  low  initial  tension  in  the  belt  for  driving  contact,  while  a  single 
drive  or  a  snub  drive  requires  a  higher  belt  tension.  These  ratios  are  given 
in  Table  21. 

In  practice,  the  two  pulleys  are  set  close  together  on  shafts  connected 
by  a  pair  of  gears  of  equal  size.  For  proper  action,  the  intermediate  tension 
Tx  (Fig.  100)  must  be  maintained,  otherwise  A  will  slip  and  fail  to  pull  the 
load.  This  may  happen  if  A  is  slightly  larger  than  B;  to  prevent  it,  care 
must  be  taken  that  A  and  B  are  turned  to  exactly  equal  diameters,  and  if 

60  -12  Ply  Belt  Full  Speed  512  Ft.per  Min.  ^^ 

Motor  300  H.P.-at  600  r.p.m. 
150H.P.,.300r.p.m. 


8  y\i  Head  Shafts  Take-up  -\     yooo  it  Weight 

Movemem-7-Feei 

FIG.  101.— Tandem  Drive  for  60-inch  12-ply  Belt.     (Robins  Conveying  Belt  Co.) 

they  are  lagged,  the  lagging  must  be  of  the  same  thickness  on  both  and  kept 
so.  Lagging  is  subject  to  wear,  and  if  the  covering  of  the  second  pulley  B 
wears  thin  from  contact  with  the  dirty  side  of  the  belt,  as  happens  when  A 
is  the  head  pulley  (see  Fig.  14),  then  the  intermediate  tension  Tx  may 
fall  off  and  cause  slippage.  If,  however,  the  lagging  on  A  wears  thin  or 
comes  off,  the  resultant  slippage  may  hurt  the  belt.  The  Robins-Hersh 
patent  of  1906  covers  the  idea  of  making  the  second  driver  slightly  larger 
than  the  first,  about  |  inch  on  the  diameter,  so  that  the  intermediate  tension 
Tx  is  always  maintained.  This  amount  of  difference  means,  with  36-inch 
drivers,  about  2  or  3  feet  slip  per  minute  at  ordinary  conveyor  speeds,  not 
enough  to  do  damage  if  the  belt  is  clean,  but  apt  to  be  injurious  if  the 
belt  is  dirty.  (See  p.  123  on  the  effect  of  slip  and  belt  creep.) 

Life  of  Tandem-driven  Belts. — In  general,  belts  used  on  tandem-driven 
conveyors  do  not  last  so  long  as  those  on  single-pulley  drives  worked  at  the 
same  tension.  The  chief  cause  is  the  reverse  bend  under  load;  secondary 
causes  are  injuries  from  accidental  slip  or  local  stretch  between  the  drivers 
and  from  the  normal  amount  of  belt  creep  (see  p.  123)  always  present  in 
tandem  drives. 

Heaviest  Belt-conveyor  Drive. — Fig.  101  shows  the  arrangement  of 
tandem-geared  pulleys  for  a  60-inch  12-ply  rubber  belt  2225  feet  long, 


TANDEM  DRIVES  ON  RETURN  RUN 


121 


driven  by  a  300-h.p.  motor.  It  was  installed  in  1917  by  Robins  for  the 
Baltimore  and  Ohio  R.  R.  at  a  eoal-shipping  pier  at  Curtis  Bay,  Baltimore, 
Md.,  and  is  probably  the  heaviest  j?elt-conveyor  drive  ever  built. 

Tandem  Drives  on  ^Return  Run. — It  often  happens  on  inclined  belt 
conveyors  or  on  long  horizontal  conveyors,  that  to  drive  at  the  head  end 
means  costly  supports  and  placing  the  machinery  in  a  dirty  or  unhandy 
place.  A  tandem  drive  on  the  return  run  near  the  foot  puts  the  machinery 
in  a  cleaner  place  where  it  is  more  likely  to  receive  proper  attention  because 
it  is  easily  accessible.  One  drawback,  not  serious,  is  the  added  tension 
necessary  to  take  care  of  the  component  of  belt  weight  due  to  the  incline 
(see  p.  118).  Other  points  to  consider  are  the  added  cost  of  the  driving 
machinery  and  bend  pulleys  as  compared  with  a  drive  at  the  head,  and  the 


FIG.  102. — Tandem  Drive  on  Return  Run  of  Conveyor. 

general  objections  to  reverse  bending  and  belt  creep  and  slip  (see  p.  123). 
Fig.  102  shows  a  typical  tandem  drive  on  the  return  run  of  a  conveyor. 

For  a  tandem  drive  in  which  one  of  the  pulleys  is  a  snub  pulley,  see 
Fig.  109. 

Lagging  Tandem  Pulleys. — From  Table  20  it  appears  that  for  a  com- 

T 

bined  wrap  of  360°  on  two  bare  iron  pulleys  the  ratio  of   —  is  4.80   and 

TZ 

that  for  rubber-lagged  pulleys  the  ratio  is  9.02.  This  shows  that  for  the 
same  slack  tension  T2  the  driving  tension  in  a  conveyor  belt  can  be  nearly 
doubled  by  lagging  the  pulleys.  For  driving  some  long  or  heavily  loaded 
belts  it  may  be  advisable  to  lag  the  pulleys  to  obtain  a  high  pull  with  a 
comparatively  slack  belt  leading  from  the  second  pulley  (as  the  belt  runs) ; 
but  in  other  cases  it  is  better  to  use  bare  pulleys  and  by  means  of  take-ups, 
screw  or  weighted,  make  T2  high  enough  to  cause  the  bare  pulleys  to  drive. 
What  this  means  in  a  practical  case  is  stated  in  Table  25  which  shows 
that  in  a  large  conveyor  belt  exerting  10,000  pounds  effective  horse- 
power pull,  Ti  must  be  increased  1300  pounds  and  772  about  the  same 
amount,  if  the  pulleys  are  bare  and  not  lagged.  This  represents  an  increase 
of  10  or  12  per  cent  in  the  belt  tension  on  the  loaded  side;  it  may  not  be 
objectionable  if  the  unit  stress  in  the  belt  is  not  excessive,  or,  in  other  words, 
if  the  pounds  pull  per  inch  per  ply  is  within  reasonable  limits  (see  p.  111). 
Of  course,  means  must  be  provided  for  giving  the  belt  the  necessary  tension 


122 


DRIVING  THE  BELT 


Tt  as  it  leaves  the  second  driver,  preferably  by  a  screw  take-up  or  a  weighted 
take-up  placed  near  the  driving  group,  as  shown  in  Figs.  6,  8  and  14,  and 
not  at  some  remote  point.  There  is  an  incidental  advantage  in  having 
means  for  adjusting  the  slack  tension  in  such  drives;  in  cold  weather  when 
the  belt  is  stiff  and  perhaps  frosty,  the  coefficient  of  belt  contact  is  low  and 
the  pulleys  may  slip  in  starting  up  for  the  day.  If  the  slack  tension  is 
increased  for  a  short  time,  the  pulleys  will  take  hold,  and  then,  after  the 
belt  has  gone  around  a  few  times  and  is  in  good  working  order,  the  tension 
can  be  reduced  to  the  normal  amount. 

TABLE  25.— COMPARISON  OF  BELT  TENSIONS  IN  TANDEM  DRIVES 


Bare  Iron  Pulleys 

Lagged  Pulleys 

Horse-power  pull 

10  000  Ibs 

10  000  Ibs 

Wrap  in  degrees  

360° 

360° 

TI  (See  Table  21) 

12  600  Ibs 

11  300  Ibs 

—  (See  Table  20)  .  . 

4  80 

9  02 

T2 
T2  

2,625  Ibs. 

1,250  Ibs. 

Increase  of  TI 

1  300  Ibs 

Increase  of  TZ  

1,375  Ibs. 

A  Disadvantage  of  Bare  Pulleys  is  that  they  wear  out  on  the  rim  if 
the  belt  handles  coke  or  similar  sharp  gritty  material  and  if  the  belt  is  not 
carefully  brushed  clean.  Bare  tandem  pulleys  on  coke  conveyors  have  been 
known  to  wear  out  in  less  than  a  year,  but  when  lagged  pulleys  were  put  in 
they  did  not  have  to  be  renewed.  The  lagging  lasted  eighteen  months, 
but  it  is  easier  and  cheaper  to  renew  lagging  than  to  replace  pulleys. 

Wear  of  Lagging. — Lagging  the  pulleys  of  tandem  drives  sometimes 
leads  to  trouble.  When  the  lagging  wears  down,  the  driving  diameter 
changes  and  it  has  happened  that  the  second  driver  working  against  the 
dirty  face  of  the  belt  wore  smaller  than  the  first 
driver,  with  consequent  slip  and  a  failure  to  drive. 
Unless  the  belt  is  brushed  clean,  fine  dirt  will  be 
deposited  on  one  of  the  drivers  and  may  accumulate 
in  thick  patches.  It  is  not  easy  to  use  a  scraper  (see 
177)  on  a  lagged  pulley  to  remove  such  crusts  and 
they  may  become  so  serious  as  to  injure  the  belt  or 
spoil  the  equality  of  belt  speed  on  the  two  drivers. 
In  some  tandem  drives  the  lagging  has  been  re- 
moved from  the  pulleys  for  that  reason,  but  this 
might  not  have  been  necessary  if  the  belt  had  been 
brushed  clean  before  its  carrying  side  touched  the 
driver. 

Another  difficulty  encountered  in  some  lagged 
tandem  drives  is  that  when  the  lagging  wears  thin,  the  bolts  which  hold 
it  project  and  are  then  apt  to  cut  and  tear  the  conveyor  belt.  Fig.  103 


FIG.  103.— Worn  Bolt 
from  Lagging  of 
Conveyor  Pulley. 


BELT  SLIP  AND  BELT  CREEP  123 

shows  such  a  bolt,  which  when  the  lagging  wore  away,  projected,  bent 
over,  and  then  rubbed  against  the  belt  until  half  of  the  head  was  worn 
away.  & 

The  remedy  for  this*  trouble  is  to  use  pulleys  with  thick  rims  and  with 
a  large  blunt-ended  drill,  remove  the  metal  from  around  the  bolt  holes  so 
that   when   the  bolt  is  drawn  tight,  it  will  pull 
the  lagging   down   into  the  countersink.     Then 
the  bolt  head  will  be  far  enough  below  the  outer 
surface  to  allow  some  wear  of  the  lagging  before 
the  bolt  head  touches  the  belt  (Fig.  104). 

Belt  Must  Be  Kept  Clean.-On  account  of     FlG 
the  movement  between  the  pulley  rims  and  the        Rim  of  Pulley  for  Lagging 
belt,  caused  by  creep  (not  necessarily  slip),  it  is        Bolts. 
very  important  to  brush  the  belt  well  and  keep 

it  clean.  It  is  cheaper  to  wear  out  brushes  than  to  wear  out  lagging  or 
the  conveyor  belt. 

Tandem  Drives :  Wear  of  Pulleys  and  Lagging. — There  are  two  factors 
that  cause  the  wear  of  pulley  rims  and  lagging  referred  to  above,  namely, 
belt  slip  and  belt  creep.  Most  persons  acquainted  with  belts  know  what 
belt  slip  is;  they  have  seen  it.  If  the  belt  stands  still  and  the  pulley  turns 
within  it,  the  slip  may  be  called  100  per  cent  of  pulley  travel  because  the 
travel  of  the  belt  has  fallen  to  zero.  When  the  pulley  begins  to  drive  the 
belt,  the  slip  is  less  and  when  the  drive  is  working  properly,  the  slip  is  least. 
In  single-pulley  drives  there  is  always  some  slip  present  (see  p.  276), 
but  in  tandem  drives  the  normal  slip  is  probably  very  small. 

Belt  Creep  is  not  so  well  understood  because  it  cannot  be  seen. 
Chapter  XX  discusses  creep  in  belt  elevators,  see  Fig.  250;  but  in  tandem 
drives  for  belt  conveyors  the  creep  is  much  greater  because  the  ratio 
of  tensions,  instead  of  being  2  or  3  to  1,  may  be  9  or  10  to  1.  A  length 
of  conveyor  belt  that  measures  12.000  inches  under  no  load  may  be 
stretched  to  12.125  inches  as  it  meets  the  first  driver;  but  on  leaving 
the  second  driver,  the  tension  may  be  'so  low  that  the  stretch  is 
practically  zero.  This  means  that  12  inches  of  belt  has  shortened  £  inch 
in  passing  through  the  drive,  and  if  the  belt  speed  is  400  feet  per 
minute,  the  creep  is  50  inches  per  minute  and  the  wear  on  the  pulley 
rim  is  represented  by  that  much  movement  of  two  surfaces  under  severe 
pressure  with  particles  of  grit  between  them.  Fifty  inches  per  minute 
does  not  seem  much,  but  it  is  the  same  as  140  miles  per  year  of  average 
service. 

Belt  creep  is  unavoidable;  it  exists  in  all  belt  conveyor  drives.  In 
plain  drives  on  iron  pulleys  it  is  least  because  the  ratio  of  tensions  is  least; 
as  the  pulling  power  of  the  drive  increases,  the  creep  increases  also  until  it 
reaches  a  maximum  in  lagged  tandem  drives.  It  must  be  said,  however, 
that  the  effect  of  creep  is  insignificant  in  most  cases;  it  is  only  where  the 
pull  is  severe  and  the  belt  dirty  that  the  wear  on  pulley  rims  or  pulley 
lagging  can  be  called  objectionable,  even  in  a  tandem  drive. 


124 


DRIVING  THE  BELT 


Effect  on  the  Belt. — So  far  as  the  belt  is  concerned,  the  wear  from  creep 
is  spread  over  a  surface  so  much  greater  than  the  surface  of  the  pulley  rim 
that  it  is  seldom  noticeable.  Since  creep  is  a  result  of  belt  stretch,  it  follows 
that  a  poorly  made  belt,  or  a  belt  too  thin  for  the  work,  will  creep  more  and 
cause  more  wear  than  a  good  belt  on  belt  surfaces  and  pulley  rims.  When 
slip  is  combined  with  creep  the  damage  is  greater;  this  may  happen  when 
heavy  conveyors,  especially  long  inclines,  are  stopped  and  then  started 
under  full  load,  when  the  slack  tension  T2  is  too  low  to  make  the  pulleys 
take  hold,  or  when  pulley  rims  are  slippery  from  frost  or  condensed  atmos- 
pheric moisture. 

Driving  by  Pressure  Belt. — Fig.  105  shows  a  method  used  by  the  Link- 
Belt  Company  for  driving  long  and  heavily  loaded  belt  conveyors  (Piez 
patent,  1919).  The  short  pressure  belt  is  maintained  under  tension  by  a 

suspended  weight  and  wraps  around  the 
driving  pulley  outside  of  the  conveyor  belt. 
No  power  is  applied  to  the  pressure  belt;  it 
merely  travels  with  the  conveyor  belt,  upon 
which  it  exerts  a  tension  depending  upon  the 
pull  in  the  pressure  belt  due  to  the  weight, 
and  on  the  angle  of  contact  between  the  two 
belts.  The  total  tension  on  the  pulling  side 
of  the  conveyor  belt  is  the  sum  of  two  items, 
one  due  to  its  own  wrap  on  the  driving  pulley, 
the  other  due  to  the  wrap  of  the  short  pressure 
belt.  Both  of  these  can  be  obtained  from 

equation  (6),  page  109.  If  T2  in  Fig.  105  represents  the  slack  tension  in 
the  conveyor  belt,  the  first  item  T^  equals  T2  XlO'00758/a,  and  if  T,  is  the 
tension  in  the  pressure  belt  where  it  leaves  the  conveyor  belt,  the  second 
item  which  we  may  call  Ts  equals  774XlO-00758/a.  Then  the  total  tension 
in  the  conveyor  belt  is  Tt  +  T3  and  if  /,  the  coefficient  of  friction  and  a  the 
angle  of  wrap  are  alike  for  both  contacts,  TV  +  TZ  =  (T2  +  2rT4)  xlO'00758/a. 
These  values  can  be  obtained  readily  from  Table  20. 

For  a  working  example,  suppose  a  conveyor  belt  has  a  wrap  of  210° 
on  a  lagged  pulley;  then  for  an  assumed  tension  of  772  =  100  pounds  on  the 
leaving  side,  the  greatest  possible  value  of  7\  on  the  opposite  side  is  100  X 
3.61  =361  pounds  for  a  single  drive  (see  Table  20).  If  the  pressure  belt 
has  a  tension  of  200  pounds  due  to  the  weight,  and  wraps  the  conveyor  belt 
for  an  angle  of  200°,  then  for  a  leaving  tension  774  =200  pounds,  the  tension 
T3  on  the  opposite  side  is  200x3.39=678  pounds  (see  Table  20).  This 
added  to  Ti  =361  pounds  makes  a  total  of  1039  pounds  for  the  pull  in  the 
conveyor  belt.  The  ratio  of  this  to  the  original  and  unchanged  slack  ten- 
sion of  100  pounds  is  10.39,  and  from  Table  20  it  is  seen  that  this  is  equiv- 
alent to  the  wrap  of  more  than  360°  and  less  than  420°:  in  other  words, 
the  device  is  equivalent,  for  the  conditions  stated,  to  a  drive  by  two  tandem- 
geared  pulleys  with  a  combined  wrap  of  over  360°. 

If,  however,  the  tension  in  the  pressure  belt  is  raised  to  500  pounds 


FIG.  105. — Pressure-belt  Drive. 


DRIVING  BY  PRESSURE  BELT 


125 


by  increasing  the  weight,  then  T3=  500x3.39  pounds  and  Ti  +  Ts=2Q5Q 
pounds.  The  ratio  of  this  to  the  assumed  slack  tension  in  the  conveyor 
belt  is  20.56,  equivalent  to  a  wr£p  of  nearly  500°  (Table  20).  It  is  prac- 
tically impossible  to  get  such  a  high  ratio  of  tensions  with  any  arrangement 
of  tandem-drive  pulleys,  and  indeed  such  high  ratios  would  be  objectionable 
in  causing  an  excessive  amount  of  belt  creep  (see  p.  123);  nevertheless  it- 
is  an  advantage  of  the  pressure-belt  drive  that  it  is  quite  easy  to  vary  the 
pulling  tension  in  the  conveyor  belt  without  disturbing  the  take-up  tension 
in  the  conveyor.  At  the  same  time,  the  drive  pulley  works  on  the  clean 
side  of  the  belt  and  belt  creep  is  not  so  likely  to  hurt  the  belt  or  the  pulley 
as  in  tandem  pulley  drives. 

Since  it  is  possible  to  get  such  high  ratios  between  slack  tension  and 
driving  tension  it  is  not  necessary  to  lag  the  driving  pulley,  because  the 
larger  part  of  the  driving  effect  can  be  obtained  by  the  contact  between  the 
pressure  belt  and  the  conveyor  belt,  with  less  dependence  on  the  contact 
between  the  latter  and  the  driving  pulley.  For  instance,  if  in  the  case 
cited  above  the  pulley  is 
bare,  ^=2.50x100=250 
pounds,  then  if  the  pres- 
sure belt  is  loaded  to  300 
pounds,  T3  =  300  X 3.39  = 
1017  pounds  and  Tl  X  T3 
=  1267  pounds.  The  ratio 
is  then  12.67  and  the  driv- 
ing effect  is  greater  than 
that  of  a  pair  of  lagged 
tandem  pulleys  with  a 
combined  wrap  of  360°. 

Fig.  106  shows  a  pres- 
sure belt  drive  applied  to 
a  40-inch  belt  conveyor 
630-foot  centers,  carrying 
600  tons  of  coarse  lime- 
stone at  300  feet  per 
minute  belt  speed.  It  has 
an  inclined  part  230  feet 
long  sloped  at  13°,  and  the 

drive  was  placed  just  at  the  bend  into  the  horizontal  run.  The  drive 
pulley  is  60  by  43  inches,  not  lagged;  the  pressure  belt  is  36  inches  wide, 
5-ply,  rubber,  loaded  to  1500  pounds  tension.  The  angle  of  wrap  is  about 
195°,  and  for  a  leaving  tension  of  2000  pounds  in  the  conveyor  belt  the 
pulling  tension  is  about  9600  pounds. 

Fig.  105  shows  how  the  pressure-belt  drive  is  applied  to  the  return  run 
of  a  belt  conveyor  with  bend  pulleys  at  A  and  B.  It  can  be  placed  at  the 
end  of  a  conveyor,  head  or.  foot,  by  using  a  bend  pulley  at  A  with  the 
head  or  foot  pulley  at  C. 


•  122/R.P.M. 

!  Puller/    V 
86-5  Ply  Belt- 
\ 15000 

i  *t/w         ^ 


15  1 42  ^ 


100  H.P.  Motor 
680  R.P.M.,, 
with  23x17  Pullc 


FIG.  106. — 40-inch  Conveyor  Belt  driven  by  Pressure 
Belt  at  Hump  on  Return  Run. 


126 


DRIVING  THE  BELT 


Page's  Auxiliary  Drive. — This  device,  patented  in  1919,  is  shown  in 
Fig.  107.  It  consists  of  a  plurality  of  independently  driven  auxiliary  belts 
in  contact  with  the  conveyor  belt  and  supported  by  the  conveyor  idlers  so 
that  the  driving  tension  is  applied  to  the  conveyor  belt  at  several  points. 
The  idea  is  that  the  maximum  tension  in  the  conveyor  belt  will  be  less  and 
that  a  very  long  belt  can  safely  be  made  lighter  and  cheaper.  No  important 
installation  of  this  device  has  been  made  (1921).  The  length  of  conveyor 
that  an  auxiliary  belt  can  be  expected  to  drive  may  be  approximated 
in  this  way.  Since  the  coefficient  of  friction  between  the  two  belts  is  not 
over  .35  and  the  coefficient  of  journal  friction  for  grease-lubricated 
idlers  is,  roughly,  about  7  per  cent  of  the  weight  of  belt  and  load,  then 
if  W  represents  the  weight  of  belt  and  load  resting  on  a  length  of 
auxiliary  belt  L,  the  greatest  pull  which  the  auxiliary  belt  can  exert  is 


FIG.   107. — Conveyor  Belt  with  Auxiliary  Drive  Belts. 

.35  TP,  and  that  will  drive  5.0L  of  conveyor  belt  beyond  the  auxiliary  drive. 
For  a  particular  case,  the  horse-power  pull  per  foot  of  conveyor  can  be 
derived  from  one  of  the  horse-power  formulas;  this  should  be  used  instead 
of  the  assumed  7  per  cent  of  weight  of  belt  and  load  in  the  approximation 
above.  One  limitation  of  this  drive  is  that  if  the  conveyor  is  loaded  for 
only  a  part  of  its  length,  or  if  the  load  runs  thin  at  intervals,  the  auxiliary 
drives  under  the  bare  places  will  exert  little  or  no  pull  on  the  conveyor 
belt. 

The  Hoy  patent  804474  of  1905  shows  a  method  of  driving  a  conveyor 
belt  by  means  of  an  inner  auxiliary  belt  when  it  is  not  convenient  to  apply 
power  to  either  of  the  end  pulleys  of  the  conveyor. 

Drive  with  Compensating  Gearing. — The  Hegeler  and  Holmes  multiple- 
pulley  drive,  patented  in  1916,  consists  of  a  compensating  planetary  gear 

device  which  distributes  power  to  two  or  three 
driving  pulleys  in  such  a  way  that  each  pulley 
exerts  an  equal  effort  in  driving  the  belt.  The 
purpose  of  the  gearing  is  the  same  as  that  of 
the  differential  gear  in  the  axle  of  a  motor 
car;  in  the  conveyor  drive  it  is  intended  to 
adjust  the  speed  of  each  pulley  for  momentary 
stretch  on  the  belt,  for  original  differences  in 
the  diameters  of  the  pulleys,  and  to  allow 

for  accidental  differences  in  pulley  diameters 
FIG.   108. — Three-pulley   Drive 
with  Compensating  Gearing.       caused    by   damp   sticky   material   forming  a 

crust  on  the  pulley  rim.     Fig.  108  shows  such 

a  three-pulley  drive  with  pulleys  1,  2,  3  and.  a  combined  angle  of  wrap 
of  634°,  designed  for  a  belt  525-foot  centers  with  a  rise  of  180  feet  on  a 


THREE-PULLEY  DRIVES  127 

20°  slope.  No  drive  with  this,  device  has  been  built;  it  is  certain  that 
the  advantages  gained  do  notf  justify  the  expense  and  the  complication  of 
the  gearing.  ^ 

Three-pulley  Drives. — The  three-pulley  drive  has  apparently  some 
advantage  in  theory,  but  it  has  never  been  used;  the  main  reason  is  that 
with  an  ordinary  two-pulley  drive  it  is  only  necessary  to  apply  some  tension 
to  the  leaving  belt  to  get  the  desired  tension  in  the  entering  belt.  For 

T 

instance,  the  ratio  of  —  for  an  angle  of  634°  is  15.9  for  bare  iron  pulleys, 
Tz 

and  48.09  for  rubber-lagged  pulleys.  Taking  the  former  ratio,  a  horse- 
power pull  of  10,000  pounds  means  that  T\  is  10,700  pounds  and  Tz  is 

—  =673  pounds,  that  is,  the  leaving  belt  is  practically  slack,  with  no 
15.9 

tension.  If  we  use  two  lagged  pulleys  with  a  combined  wrap  of  360°  we 
avoid  the  complication  of  the  third  pulley  with  its  gearing,  and  the  belt 

T 

creep  inseparable  from  a  high  ratio  of  — .     Then    from    Table  21,   T\  is 

Tz 

11,300  pounds  and  Ts  is  1250  pounds.  That  is,  by  increasing  the  belt 
tension  only  600  pounds,  we  can  make  two  pulleys  do  the  work,  and  do  it 
better. 

T 
Size  of  Pulleys. — In  the  formula  on  page  109,  —  =  I0-00758/a,  the  only 

TZ 

variables  which  determine  the  tractive  force  are  the  angle  of  wrap  and  the 
coefficient  of  friction;  the  diameter  of  the  pulley  does  not  enter  into  the 
calculation.  Some  have  thought  that  a  large  pulley  gets  a  better  grip  on  a 
belt  than  a  smaller  pulley,  but  within  the  limits  of  good  practice  that  is 
not  true. 

Haddock's  experiments  (Transactions,  A.  S.  M.  E.,  1908)  with  a  12-inch 
4-ply  rubber  belt  showed  no  variation  in  tractive  force  whether  it  was 
driven  by  a  42-inch  pulley  or  a  20-inch  pulley,  but  on  a  12-inch  pulley  the 
traction  dropped  20  per  cent.  That  was  because  the  4-ply  belt  was  too  stiff 
to  bend  to  the  12-inch  diameter  without  loss  of  contact  pressure.  These 
experiments  established  the  rule  that  the  diameter  of  the  drive  pulley  should 
be  at  least  five  times  the  number  of  plies  in  the  belt.  When  a  pulley  acts 
as  a  guide  or  a  deflector,  as  at  a  foot  shaft  or  a  snub  shaft,  it  is  considered 
proper  to  make  the  diameter  three  or  four  times  the  number  of  plies,  but, 
in  any  case,  the  larger  the  better. 

The  objection  to  making  the  ratio  larger  than  5  to  1  for  drivers  is  that 
the  pulleys  take  up  more  room  and  cost  more,  and  more  gearing  or  larger 
gearing  is  required  because  the  larger  pulley  makes  fewer  turns  for  the 
same  conveyor  speed.  On  the  other  hand,  a  diameter  larger  than  that 
given  by  the  5-to-l  ratio  stresses  the  friction  between  the  plies  less,  makes 
it  less  liable  to  crack  when  old  and  hence  postpones  the  day  when  the 
belt  fails  by  separation  of  the  plies.  (For  an  instance,  see  p.  117.) 

An  incidental  advantage  of  a  large  head  pulley  is  that  when  it  is  used 


128  DRIVING  THE  BELT 

with  a  snub  pulley  the  angle  of  belt  wrap  can  be  made  large  without  having 
the  snub  pulley  too  small. 

When  the  ratio  for  a  driver  is  less  than  4  to  1  the  belt  tension  must  be 
increased  to  make  the  belt  hug  the  pulley  tight  enough  to  drive.  This  in 
itself  is  a  disadvantage,  but  the  greater  harm  is  the  excessive  stretch  in  the 
friction  layers  between  the  plies  and  the  greater  tendency  for  the  plies 
to  come  apart  when  the  friction  gets  old. 

Pulley  Rims. — All  drive  pulleys,  foot  pulleys  and  snub  pulleys  should  be 
specified  as  "  double-belt  "  pulleys  with  a  "  crown  "  on  the  pulley  face 
of  at  least  f  inch  per  foot  of  face.  A  heavy  crown  will  keep  the  belt  centered 
even  if  the  shaft  on  which  the  pulley  is  mounted  should  get  out  of  level 
or  out  of  square  with  the  belt;  hence  some  designers  specify  -f$-  or  £-inch 
crown  per  foot  of  face  for  drive  pulleys  where  the  belt  might  tend  to  get 
out  of  line.  Pulleys  wider  than  24  or  30  inches  should  have  double  arms. 
The  faces  should  be  2  inches  wider  than  the  belts  up  to  18  inches,  3  inches 
more  for  24-  or  30-inch  belts  and  4  inches  more  than  belt  width  in  the 
wider  belts.  This  excess  of  width  permits  the  belt  to  run  out  of  center 
for  a  few  inches  without  requiring  it  to  be  "  trained  "  back  into  position 
by  adjusting  the  troughing  idlers  or  forcing  it  back  by  the  use  of  edge  rolls. 
It  is  quite  necessary  where  the  conveyor  head  or  foot  is  supported  on  a 
frame  which  may  settle  or  get  out  of  line  or  where  the  conveyor  runway  is 
not  permanently  aligned.  A  few  inches  of  excess  width  on  the  troughing 
and  return  idlers  is  also  worth  having  under  such  conditions.  It  is  better 
to  incur  that  expense  than  to  ruin  a  belt  by  the  use  of  side-guide  idlers  or 
to  damage  the  pulley  side  by  skewing  the  troughing  rolls  to  an  excessive 
angle.  For  very  heavy  pulls,  the  rims  of  drive  pulleys  should  have  inside 
flanges  for  reinforcement. 

Snub  Pulleys. — If  a  conveyor  belt  makes  a  wrap  of  180°  on  an  iron 

pulley  the  tension  Tt  in  the  empty  belt  must  be. =  .456  of  that  on  the 

2.  i  y 

loaded  side  (see  Table  20,  p.  109).  If  the  useful  pull  or  horse-power  pull 
is  2000  pounds,  the  total  tension  Ti  on  the  tight  or  loaded  side  must  be  2000  X 
1.84=3680  pounds  (see  Table  21,  p.  110),  and  therefore  the  pull  on 
the  empty  side  is  3680 X. 456  =  1680  pounds.  But  if  a  snub  pulley  (see 
Fig.  11)  is  used  to  increase  the  angle  of  wrap  to  240°,  the  total  belt  tension 
Ti  is,  for  the  same  work,  3100  pounds,  and  the  pull  on  the  empty  side  T* 
is  1100  pounds,  a  reduction  of  nearly  600  pounds  in  the  belt  tension,  equiv- 
alent to  1  ply  of  a  24-inch  belt.  This  is  the  advantage  of  using  a  snub 
pulley ;  to  offset  it,  there  is  the  expense  of  the  pulley  and  the  reverse  bend- 
ing of  the  belt,  also  the  tendency  for  sharp  particles  adhering  to  the  belt 
to  be  forced  into  the  cover  by  contact  with  the  snub  pulley. 

For  most  horizontal  conveyors  handling  coal  a  snub  pulley  is  not  required, 
and  in  other  conveyors  handling  heavier  materials  it  may  be  better  to  work 
the  belt  at  a  tension  a  little  higher  than  normal  rather  than  install  a  snub 
pulley.  (For  an  example,  see  page  117.) 

Sometimes  the  thickness  of  the  belt  will  be  made  greater  than  is  necessary 


-DEFLECTOR  PULLEYS 


129 


1  Eleutric  Motor 

2  First  Countershaft 

3  Second 

4  Headshaft  -  3o"Belt  Pulley 
6    Snubshaft :  -  12  Belt  Pullej 

and  geared  to  Headshaft 
ratio  of  Gears  43  to  106 
6    Weighted  Take-up 


FIG.  109.— Snub-shaft  Geared  to  Head 
Shaft  and  Acting  as  Second  Pulley  of 
Tandem  Drive.  (Lamson  Company.) 


to  transmit  the  pull ;  then  it  may.  be  able  to  bear  the  tension  necessary  to 
get  driving  contact  without  thte  use  of  a  snub  pulley.  (For  reasons  for 
increasing  the  number  of  plies,  sdte  Table  24  and  p.  114.) 

On  conveyors  handling  materials  which  stick  to  the  belt,  a  snub  pulley 
is  apt  to  receive  a  crust  or  layer  which  may  build  up  so  as  to  be  objection- 
able. A  steel  scraper  bearing  against  the  face  of  the  pulley  will  prevent 
it  (see  Figs.  177  and  178). 

It  is  possible  to  gear  a  snub  shaft  to  a  head  shaft  and  make  the  snub 
pulley  help  to  drive  the  belt.  Such 
a  drive  is  shown  in  Fig.  109,  which 
illustrates  the  arrangement  at  the  head 
of  a  number  of  package  conveyors  in 
the  Chicago  Railway  Post  Office  Ter- 
minal (1922).  This  gives  a  driving 
wrap  of  160°  on  the  snub  pulley  and 
240°  on  the  head  pulley.  It  is  in 
effect  a  tandem  drive  with  the  speeds 
of  the  shafts  in  the  inverse  ratio  of 
their  pulley  diameters.  The  belts  are 
stitched  canvas,  4  or  5  ply,  36  to  48 
inches  wide,  of  32  ounce  duck. 

Deflector  pulleys  around  which  the  conveyor  pull  is  transmitted  should 
be  -as  large  as  drive  pulleys,  that  is,  5-inch  diameter  per  ply  of  belt.  Other 
pulleys  can  be  3  or  4  inches  per  ply  of  belt.  An  instance  where  the  total 
pull  is  transmitted  around  deflector  pulleys  is  shown  in  Fig.  110,  representing 
an  inclined  coke  conveyor  driven  at  the  foot  B.  Instead  of  making  the  head 
and  foot  pulleys  A  and  B  36  inches  and  the  deflector  and  take-up  pulleys 

C  and   D  24  inches  it  would  have 

A      t      tt        r% 

been  better  to  make  all  36  inches, 
or  at  least  all  30  inches  because 
the  belt  was  under  practically  the 
same  tension  in  passing  around  all 
of  them.  The  deflector  E  was  16 
inches  in  diameter,  but  24  inches 
would  have  been  better  for  a  similar 
reason.  The  belt  in  this  case  was 
36  inches  wide,  6  plies  of  28-ounce 
duck,  although  the  work  required 
only  2  plies  to  take  care  of  the 

maximum  tension  TV  It  lasted  fourteen  months  and  carried  240,000  tons 
of  crushed  coke  at  a  cost  of  one-ninth  of  a  cent  per  ton,  a  fairly  good 
record;  but  if  the  pulleys  had  been  larger  it  might  have  lasted  longer 
than  it  did.  Its  fourteen  months  of  service  were  not  enough  to  make  it 
die  of  old  age.  (For  a  suggested  improvement,  see  page  119.) 

Curves  in  Belt  Conveyors. — Fig.  Ill  represents  a  belt  conveyor  AD, 
partly  inclined  and  partly  horizontal  or  at  two  different  angles  of  inclina- 


Taie-up 


FIG.  110.— Conveyor  with  Deflector  Pulleys 
too  Small  in  Diameter. 


130  DRIVING  THE  BELT 

tion;  the  problem  is  to  find  the  radius  EB  of  the  curve  BC  joining  the  two 
straight  portions,  which  is  large  enough  to  prevent  the  belt  from  lifting 
off  the  idlers  in  the  section  BC  under  the  most  unfavorable  condition, 
namely,  when  the  section  A  B  is  fully  loaded  and  the  rest  of  the  conveyor 

x2 
is  empty.     The  curve  BC  is  part  of  a  catenary  whose  equation  is  y  = — 

(Marks'  M.  E.   Handbook,  1st  ed.,  p. 

T 

148)  where  a  = —  and  T  is  the  tension 
W 

at  B  in   pounds  and  W  is  the  weight 
per  foot  of  the  empty  belt  in  pounds. 

Wx* 
Therefore  y  = .     The  angle   A   of 

the  inclined  portion  CD  is  determined 
FIG.  111. — Radius  of  Curvature  for  2?/      W 

Bends  in  Belt  Conveyors.  by  tang  A  =—  = —  X  and  the  radius 

T 

of  curvature  is  EB  = —  since  the  flat  catenary  is  nearly  a  parabola. 
W 

Values  of  W  are  given  on  in  Tables  4, 5, 6, 7, 8.  To  estimate  Ti  the  pull  at  B, 
consider  AB  as  a  loaded  conveyor,  and  calculate  the  horse-power  and  then 
the  horse-power  pull  corresponding  to  the  belt  speed  (see  p.  108).  Then 
according  to  the  method  of  driving  the  conveyor  at  D  or  elsewhere,  mul- 
tiply this  horse-power  pull  by  the  proper  factor  from  Table  21,  page  110. 
If  the  inclination  of  CD  is  less  than  4°,  add  for  the  pull  on  the  return  side 
of  the  incline  7  per  cent  of  the  weight  of  the  belt  on  the  lower  run  of  the 

T 
incline   (see  Table  22,  p.  113).     To  the  radius  —  add  something  to  provide 

for  the  chance  that  the  take-up  tension  may  be  increased  at  times  and  the 
belt  may  be  more  likely  to  lift  off  the  idlers  at  the  curve.  This  tension  may 
be  increased  accidentally  by  careless  use  of  the  take-ups  or  intentionally 
to  give  the  necessary  slack  tension  at  the  head  to  overcome  slippage  of  the 
belt  or  to  provide  for  extra  heavy  loading  of  the  belt. 

If  such  a  conveyor  is  driven  at  A  or  at  some  place  on  the  return  side  near 
A,  the  curve  for  the  lower  run  must  be  calculated  from  the  total  horse- 
power pull  for  the  conveyor,  or  it  may  be  more  convenient  to  run  the  belt 
under  a  bend  pulley  between  two  straight  runs  on  the  lower  side  and  curve 
the  upper  run  only. 

Bends  over  Pulleys. — Where  pulleys  are  used  to  change  the  direction 
of  travel  of  belts  under  working  tension  they  should  be  double-belt  straight- 
face  pulleys  at  least  4  inches  in  diameter  for  each  ply  of  belt.  (For  the  use 
of  troughing  pulleys  at  humps,  see  p,  74.) 


CHAPTER  VI 
TENSION  AND  TAKE-UP  DEVICES 

Take-ups  for  Belt  Conveyors. — A  take-up  does  two  things;  it  removes 
the  accumulation  of  slack  in  the  belt  and  permits  the  belt  to  be  stressed  to 
the  tension  at  which  the  pulley  will  drive  it.  If  the  take-up  is  of  the 
weighted  or  automatic  type  (Fig.  112)  it  must  carry  enough  weight  to  load 
the  empty  belt  to  the  tension  Tz  at  which  the  pulley  can  pull  the  load; 
thus,  if  a  belt  driven  by  a  wrap  of  210°  on  a  lagged  pulley  has  a  total  tension 


of  2000  pounds  on  the  pulling  side,  the  idle  tension  T*  is 


2000 
.361 


=  550 


pounds  (see  Table  20,  p.  109)  and  when  arranged  like  Fig.  112  the  suspended 
weight  of  the  pulley  and  its  attachments  must  be  1100  pounds  to  give  the 
belt  the  necessary  tension.  By  the  same  reasoning,  if  the  weight  is  applied 

to  a  foot-take-up,  it  must   be   twice    the 
amount  of  the  idle  tension  772. 

A  suspended  or  "  gravity  "  take-up  like 
Fig.  112  can  be  placed  anywhere  on  the 
return  belt.  It  requires  little  attention 
and  keeps  an  even  tension  in  the  belt.  The 
objection  to  it  is  that  it  gives  the  belt  three 
extra  bends. 


FIG.  112.—"  Gravity  "  Take-up 
for  Belt  Conveyor. 


FIG.  113.— Screw  Take-up. 


A  screw  take-up  (Fig.  113)  is  simpler  and  cheaper  and  when  placed 
at  the  foot  of  the  conveyor  it  requires  no  extra  bends  in  the  belt.  In 
the  hands  of  a  careless  man,  a  screw  take-up  may  pull  a  belt  much  tighter 
than  is  necessary  for  driving  contact,  and  thereby  injure  it  or  pull  the 
lacing  apart.  On  the  other  hand,  if  the  accumulation  of  stretch  is  not 
removed  as  it  forms,  the  slack  tension  at  the  driver  may  become  too  low; 
then  when  the  belt  slips,  it  may  be  scraped  or  torn  on  the  pulley  side. 

In  a  tandem  pulley  drive  (Fig.  102)  or  a  drive  with  a  pressure  belt 

T 

(Fig.  105)  the  ratio  of  —  is  high,  and  for  a  given  horse-power  pull  Tz  is 
T  2 

comparatively  low  (see  Table  25,  p,  122);  hence  the  belt  coming  from  such 

131 


132 


TENSION  AND  TAKE-UP  DEVICES 


a  drive  may  be  under  very  low  tension.  When  such  drives  are  near  the  foot 
of  a  conveyor  it  may  be  convenient  to  let  the  belt  hang  slack  between  the 
driver  and  the  foot;  then  with  screw  take-ups  at  the  foot  it  is  possible  to 
maintain  an  even  tension  in  the  belt  by  keeping  the  sag  uniform.  A  look 
at  the  hang  of  the  belt  will  show  whether  it  is  at  the  right  tension  or  not. 
In  general,  the  best  place  for  a  take-up  is  where  the  belt  tension  is  low. 
One  disadvantage  of  driving  a  conveyor  at  the  foot  pulley  is  the  difficulty 
of  disposing  of  the  slack  belt.  (For  an  instance  of  this,  see  Fig.  110, 
p.  129,) 


PIG.  114. — Weighted  Pull  Take-up  for  Grain  Belt.     (James  Stewart  &  Co.,  Inc.) 

Weighted  Pull  Take-ups. — Fig.  101,  page  120,  shows  a  take-up  for  a 
60-inch  12-ply  belt  placed  next  to  the  driving  end  of  a  conveyor  over  1000- 
foot  centers. 

Fig.  114  shows  the  foot  of  a  grain  conveyor  with  an  automatic  take-up, 
The  sheave  in  the  corner  is  mounted  on  a  pipe  shaft  to  which  are  fastened 
two  ropes  leading  to  the  shaft  bearings.  The  weight  rope  makes  a  number 
of  turns  around  the  sheave,  and  as  the  weight  descends,  the  take-up  ropes 
are  wound  upon  the  pipe  under  a  tension  equal  to  five  or  six  times  the 
weight. 


CHAPTER  VII 


LOADING  THE  BELT 


Loading  Chutes. — Besides  the  normal  duty  of  conveying  material,  a 
belt  has  to  check  the  impact  of  material  at  the  feed  point  and  impart  to  it 
the  belt's  own  velocity  in  the  direction  of  travel.  If  200  pounds  of  material 
falls  from  a  height  of  5  feet  on  a  belt,  the  belt  must  absorb  within  its  structure 
1000  foot-pounds  of  energy  in  stopping  its  fall.  It  does  it  through  the 
elasticity  of  its  body  of  fabric  and  of  its  cover,  if  it  has  a  cover.  If  there  are 
hard  sharp  lumps,  some  of  the  energy  of  the  falling  mass  is  expended  in 
cutting  the  belt  or  its  cover,  es- 
pecially if  the  belt  is  so  supported 
that  it  cannot  exert  its  elasticity. 
This  happens  if  an  idler  is  placed 
directly  under  the  point  of  impact. 
To  avoid  it,  the  arrangement  should 
be  like  Fig.  115.  The  idler  A  avoids 
the  direct  impact,  yet  it  prevents 
the  belt  from  sagging  too  far  from 
the  skirt-boards  B.  If  the  belt 
were  fed  midway  between  two 
idlers,  there  might  be  too  much 


FIG.  115. — Loading  Chute  and  Skirt  Boards. 


deflection  of  the  belt  from  impact,  with  consequent  leakage  sideways  under 
the  skirt-boards.  If  the  idler  is  directly  under  the  point  of  impact,  there  is 
the  added  risk  of  breaking  the  idler,  see  also  Fig.  73. 

If,  in  the  case  referred  to  above,  the  conveyor  runs  5.  feet  per  second, 
the  work  it  does  in  bringing  the  200  pounds  from  zero  velocity  to  300  feet 

1      200 
per  minute  is  -  X 52  =78  foot-pounds,  and  if  the  200  pounds  is  fed  on 


in  two  seconds,  the  equivalent  is 


78X60 


=  .07  h.p.  for  the  capacity  of 


2X33,000 

180  tons  per  hour.  While  this  represents  only  a  small  addition  to  the 
normal  pull  in  the  belt,  its  effect  on  the  carrying  surface  can  be  understood 
if  we  imagine  a  grinding  wheel  made  of  the  material  carried,  pressed  against 
the  belt  and  driven  by  .07  h.p.  for  every  minute  the  conveyor  runs.  Of 
course,  some  of  the  material  falls  on  itself  and  does  not  touch  the  belt,  but 
the  example  will  serve  to  emphasize  the  statement  that  the  arrangement 
of  the  feed  is  a  very  important  item  in  the  design  of  the  conveyor  and 
that  a  poor  feed  may  spoil  a  good  belt. 

133 


134 


LOADING  THE  BELT 


Proper  Angles  for  Loading  Chutes. — If  belts  could  be  fed  with 
material  moving  at  belt  velocity  (Fig.  116),  cutting  and  abrasion  would 
be  at  a  minimum;  but  it  is  seldom  possible  in  practice.  The  best 
that  can  be  done  is  to  deliver  material  through  a  chute  pointing  in 
the  direction  of  belt  travel  and  at  such  an  angle  that  the  horizontal 
component  of  the  velocity  in  the  chute  will  be  equal  to  belt  speed. 
If,  as  in  Fig.  117,  the  velocity  of  the  belt  is  V,  the  theoretical  belt  velocity 
of  material  in  the  chute  is  V  secant  A ;  the  horizontal  component  of  this  is 
V  secant  A  cosine  A  which  =  V,  and  the  vertical  component  which  is  a 
measure  of  the  impact  on  the  belt  is  V  secant  A  sine  A.  In  practice,  the 
best  angle  of  chute  can  be  determined  only  by  trial ;  grain  flows  easily  in 
chutes  sloped  6  in  12  (27°)  and  rapidly  at  8  in  12  (34°);  but  in  Westmacott 
&  Lyster's  experiments  in  1865  (see  p.  7)  it  appeared  that  the  best  angle 
for  delivering  wheat  to  a  belt  moving  at  500  feet  per  minute  was  42  £°. 
Anthracite  coal  in  the  domestic  sizes  flows  readily  in  steel  chutes  at  5^ 
in  12  (25°),  and  in  the  steam  sizes  at  7  in  12  (30°),  crushed  soft  coal  requires 


FIG.  116. — Theoretical  Feed  with  Minimum  FIG.   117. — Relation  of  Belt  Velocity 

of  Abrasion.  to  Flow  in  Chute. 

8i  in  12  (35°).  Screened  and  sized  stone  or  ore  will  flow  in  steel  chutes  at 
7  in  12  (30°),  the  same  material  mixed  with  fine  stuff  requires  85  in  21 
(35°).  For  all  of  these  the  slope  of  the  loading  chute  should  be  5°  or  10° 
steeper,  but  for  large  lump  coal  or  ore  the  angle  should  not  exceed  45° 
(12  in  12);  beyond  that  the  lumps  will  not  slide  on  the  bottom  of  the 
chute,  but  descend  in  a  series  of  jumps.  Another  factor  with  lumpy  or 
sharp  material  is  that  in  a  steep  chute  the  vertical  component  of  its  velocity 
becomes  too  great  and  the  belt  may  be  cut  by  the  impact.  To  prevent 
that,  the  chute  may  be  curved  as  in  Fig.  123,  or  if  the  chute  is  long  enough 
to  give  the  material  the  necessary  momentum,  the  angle  may  be  broken, 
as  in  Fig.  115. 

Both  of  these  methods  are  effective  in  preventing,  in  some  degree,  the 
effect  of  impact  and  in  giving  the  material  some  velocity  in  the  direction 
of  belt  travel. 

A  form  of  chute  used  in  loading  run-of-mine  coal  on  a  60-inch  belt  is 
shown  in  Fig.  118.  The  rounded  bottom  does  not  interfere  with  the  flow 
of  fine  coal  or  pieces  of  moderate  size,  but  lumps  of  very  large  size  are  apt 


SCREEN  CHUTES 


135 


to  be  directed  forward  and  upward  by  the  converging  corners  so  that  they 
will  strike  the  belt  at  B  after  it  has  already  received  a  layer  of  the  smaller 
coal  at  A.  Another  method  of  djaing  the  same  thing  is  shown  in  Fig.  119. 


u 


o 


o 


Section  on  Center  line  of  Conveyor  and  Chute 


Chute 


PLAN   VILW 


FIG.   118.— Belt  Loading  Chute  for  Run-of-Mine  Coal. 

Screen  Chutes. — From  the  earliest  days  of  the  business,  efforts  have 
been  made  to  reduce  the  wear  on  the  belt  surface  by  screening  out  the  fines 

in  the  loading   chute  and  delivering    „ 

them  to  the  belt  first,  so  as  to  cushion 

the  fall  of  the  lumps.     Fig.  120  shows     (          Beit 

the  idea,  but  it  is   not   easy  to  avoid 

choking  such  a  chute;    even   if   bars 

are  used  instead  of  perforated  plate, 

pieces  stick  between   them    and    the 

chute  chokes  or  else  the  velocity  of 

flow  through  it  is  reduced.     Another 

construction  is  to   put  finger  bars  on 

the  end  of  the  chute  and  let  the  fines 

fall   between,   while   the    lumps    ride 

over,  but  this  is  open  to  the  danger 

of  pieces  catching  between  the  bars 

or  under  them  and   dragging  on  the 

belt. 


fcelt 


When  a  belt  is  inclined  at  an  angle    IG*  L1^;  , 

a  Belt  from  Impact  of  Large  Lumps. 

close  to  20    it  is  not  easy  to  deliver 

material  to  it  at  belt  speed;  the  lumps  tumble  around  longer  before  becom- 
ing settled  and  the  wear  on  the  belt  surface  is  greater.     In  such  cases  a 


136 


LOADING  THE  BELT 


screen  chute,  is  a  good  thing  if  it  is  properly  made.  Figs.  121  and  122  show 
one  designed  to  transfer  run-of-mine  coal  from  an  apron  feeder  to  a  36-inch 
belt  inclined  at  20°.  The  screening  surface  was  about  30  by  50  inches,  the 

bars  were  4  inches  by  £  inch  spaced 
3  inches;  the  spacers  between  the 
bars  were  set  low  to  keep  clear  of 
lumps  riding  over  the  bars  and  the 
apron  plate  A  was  set  below  the  top 
surface  of  the  bars  for  the  same  reason. 
Since  the  bars  did  not  extend  close  to 
the  belt,  there  was  no  danger  that 
lumps  caught  between  the  bars  would 
drag  on  the  belt  and  injure  it.  The 
main  discharge  from  the  apron  feeder 
fell  on  the  screen  bars  while  the  dribble  under  the  head  wheel  was  caught 
in  the  side  extension  of  the  chute  and  put  on  the  belt  behind  the  screen 
bars. 

Fig.  123  shows  a  similar  chute  without  the  screen  bars  but  with  a  curved 
bottom  designed  to  catch  the  lumps  falling  over  the  head  of  an  apron 


FIG.  120. — Typical  Screen  Chute. 


FIG.  121. — Screen  Chute  for  Loading  an 
Inclined  Belt  Conveyor. 


FIG.   122.— End  View  of  Screen  Chute 
Shown  in  Fig.  121. 


feeder  and  deliver  them  to  a  36-inch  belt  at  belt  speed.  Some  of  the 
discharge  from  the  apron  conveyor,  including  the  drip,  falls  into  the  side 
extension  chute  and  is  put  on  to  the  belt  before  the  lumps  so  that  the  large 
pieces  fall  on  a  cushion  of  small  coal. 

Transfer  Chutes. — In  designing  chutes  to  transfer  from  one  conveyor 
to  another,  care  should  be  taken  that  the  discharge  from  the  first  belt  cannot 
fall  clear  through  on  to  the  second  belt  without  being  guided  by  the  chute, 
and  also  that  the  material  is  loaded  with  the  run  of  the  belt  and  not  side- 
ways. A  belt  loaded  from  the  side  will  suffer  from  cutting  and  abrasion; 


SKIRT-BOARDS 


137 


it  is  apt  to  leak  under  the  skirt-boards,  and  with  an  unsymmetrical  cross- 
section  of  load  it  will  run  crookecl  and  need  the  assistance  of  side-guide 
idlers  to  keep  it  in  place.  ^ 

Skirt-boards. — When"  a  horizontal  conveyor  is  loaded  by  a  properly 
designed  chute  it  should  not  be  necessary  to  extend  the  sides  of  the  chute 
more  than  3or4feet  to  confine  the  material  while  it  is  coming  up  to  belt  speed 
and  to  prevent  lumps  from  rolling  off.  These  extensions  should  be  kept  a 
few  inches  above  the  surface  of  the  belt  and  the  space  closed  by  a  strip  of 
rubber  belt  to  prevent  fine  stuff  from  scattering  and  lumps  from  getting 

under  the  edge  of  the  skirt-boards 
and  jamming  there.  With  steel  skirt- 
boards  the  risk  of  jamming  is  less  than 
with  wood.  In  loading  run-of-mine 
or  crushed  coal  onto  belts  36  inches 
or  wider,  where  the  width  between 
chute  sides  or  skirt-boards  is  not  over 
IW(W  =  width  of  belt),  the  rubber 


T 


Put  of  Discharge  fn 
j^pron  Conveyor  Fed  to  Belt  Here 

Foot  of  42  Belt 
<i7&'per  Min.  600  Ions  P.H. 


FIG.  123. — Curved-bottom  Chute  fpr  Load- 
ing an  Inclined  Belt  Conveyor. 


FIG.   124. — Wooden  Skirt-boards  with 
Rubber  Belt  Guard  Strips. 


strips  can  often  be  omitted,  because  then  there  is  margin  enough  between 
the  chute  and  the  edge  of  the  belt  to  prevent  loss  of  material.  Fig.  124 
shows  a  typical  cross-section  of  wooden  skirt-boards.  Fig.  115  gives  a 
design  in  steel  construction.  The  chute  shown  in  Fig.  118  has  no  skirt- 
boards  or  rubber  strips. 

Damage  from  Skirt-boards. — Nearly  everyone  in  the  belt  conveyor 
business  can  think  of  cases  where  belts  have  been  split  or  seriously  injured 
by  skirt-boards  or  chutes  getting  out  of  adjustment.  To  lessen  the  risk, 
skirt-boards  should  be  firmly  supported.  /They  should  be  no  longer  than 
is  necessary  and  there  should  be  clearance  enough  under  them  to  avoid 
cutting  or  scraping  the  belt  if  the  latter,  when  running  empty,  should 
not  lie  down  properly  on  the  horizontal  pulleys  of  the  idlers.  Means  -should 
also  be  used  to  prevent  trippers  from  coming  so  close  to  the  chute  as  to 
lift  the  belt  under  it  (see  p.  169). 

Skirt-boards  for  Inclined  Conveyors. — When  the  angle  of  inclination 
is  over  10°  the  material  does  not  acquire  belt  speed  so  readily,  and  lumps 
roll  around  more  before  becoming  settled.  For  that  reason,  it  is  generally 


138 


LOADING  THE  BELT 


necessary  to  make  skirt-boards  longer  than  for  horizontal  conveyors.  If 
the  incline  is  merely  a  short  portion  of  the  conveyor  depressed  to  limit  the 
travel  of  the  tripper  (see  p.  170)  the  boards  are  sometimes  extended  to 
the  hump  (Fig.  133)  to  prevent  loss  of  material  there  when  the  belt  flattens 
out  in  going  over  the  flat-faced  pulley.  But  unless  the  sides  are  made  con- 
tinuous with  those  at  the  loading  point,  it  is  not  safe  to  use  skirt-boards 
at  such  humps,  because  material  is  sure  to  catch  under  them.  When  belts 
are  loaded  to  their  standard  ratings  (see  Figs.  133  and  137)  there  should  be 

no  spill  in  passing  over  hump  pulleys 
even  though  some  of  the  material  does 
describe  a  short  trajectory  and  rise  from 
the  belt  just  as  it  passes  the  bend.  In 
any  case,  it  is  better  to  reduce  the  load 
cross-section  than  to  use  separate  skirt- 
boards  at  humps. 

In  order  to  remove  all  danger  of 
lumps  rolling  off  the  belt,  skirt-boards 
for  steep  inclines  are  sometimes  run  the 
full  length  of  the  conveyor.  Fig.  125 
shows  continuous  guards  of  2-by-12- 
inch  planks  for  a  36-inch  conveyor, 
180  feet  long  inclined  20°.  The  bottom 
edges  of  the  guards  should  be  set  above 
the  belt  so  that  if  the  belt  shifts  to 
one  side  it  cannot  rub  against  them  nor  their  supports.  For  continuous 
guards  on  a  grain  belt,  see  Fig.  141. 

In  feeding  dry,  dusty  material  to  a  belt  it  is  sometimes  advisable  to 
extend  the  skirt-boards  and  put  a  cover  over  them  to  make  a  box  long 


FIG. 


SECTION  A-A 

125. — Continuous  Skirt-boards  for 
an  Inclined  Belt  Conveyor. 


FIG.  126. — Covered  Skirt-boards  for  Dusty  Material. 

enough  to  confine  the  dust.     Fig.  126  shows  such  a  guard  for  a  36-inch 
belt  handling  pulverized  coal  at  a  by-product  coke  plant. 

Design  of  Skirt-boards. — It  is  not  usually  practicable  to  let  skirt-boards 
diverge  or  spread  apart  with  the  run  of  the  belt  because  the  lower  edges 
would  have  to  be  trimmed  to  a  curve  to  suit  the  contour  of  the  belt  on  the 


BELT  CONVEYOR  FEEDERS 


139 


troughing  idlers.  There  might  be  some  gain  in  flaring  the  skirt-boards 
because  the  friction  between  theni  and  the  material  would  then  be  reduced  ; 
but  the  practical  gain  would  be^mall  and  there  would  be  the  risk  that 
accidental  variations  in*the  contour  of  the  belt  due  to  belt  tension  or  the 
load  of  material  would  cause  rubbing  against  the  lower  edges  of  the  boards. 
It  is  better  to  keep  the  boards  parallel  and  in  the  design  of  the  loading 
arrangements,  provide  a  support  that  will  definitely  fix  the  position  of  the 
skirt-boards  with  reference  to  the  belt.  If  the  design  of  the  skirt-boards 
and  their  supports  is  left  to  chance  or  to  a  millwright  new  to  such  work, 
the  job  is  not  likely  to  be  done  right. 

Feeding  as  Related  to  Belt  Capacity.  —  The  ordinary  formulas  for  belt 
capacity  (see  p.  143)  allow  for  some  irregularity  in  feed,  and  even  for  some 
bare  places  on  the  belt  occasionally;  but  for  the  best  results  the  feed  should 
be  under  control  so  that  the  load  cross-section  is  uniform  from  end  to  end. 
With  that  arranged,  the  speed  of  the  belt  can  be  reduced  below  what  the 
ordinary  tables  give  and  still  the  conveyor  will  deliver  its  rated  load,  or  if 
necessary  the  belt  can  be  run  at  a  standard  speed  and  convey  more  material 


~(o)  0  0 

FIG.  127.  —  Screw  Feeder. 


FIG.  128.  —  Apron  Feeder. 


than  the  standard  rating.  (For  load  cross-sections  as  related  to  width  of 
belt,  see  Figs.  133,  to  137.) 

If  the  material  is  fine  and  lively  a  simple  slide  gate  in  a  chute  will  control 
its  flow,  but  this  is  not  possible  with  lumps  nor  when  lumps  are  mixed 
with  fine  stuff.  For  these  some  kind  of  feeder  is  necessary,  especially  when 
the  material  is  drawn  from  bins  or  from  track-hoppers.  When  crushers  or 
pulverizers  deliver  to  belt  conveyors  it  is  usually  best  to  put  the  feeder 
over  the  crusher  and  then  provide  a  hopper  or  a  chute  beneath  it  large 
enough  to  equalize  any  momentary  rush  of  fine  stuff  through  the  crusher. 

Belt  Conveyor  Feeders.  —  To  pile  an  even  load  on  the  belt,  the  best 
feeder  is  one  which  has  a  steady  forward  delivery.  The  screw  feeder 
(Fig.  127)  will  handle  fine  stuff,  moist  or  dry,  but  it  is  not  long-lived  in 
gritty  material  and  it  is  apt  to  be  damaged  if  sticks,  tools  or  large  lumps 
accidentally  get  into  it.  The  apron  feeder  (Fig.  128)  gives  a  steady  feed  of 
any  kind  of  material  up  to  the  largest  lump  of  mined  coal  or  ore.  For 
heavy  material  it  becomes  costly.  The  reciprocating  plate  feeder  (Fig.  129) 
is  simple  and  cheap;  it  can  be  placed  directly  under  a  track  hopper  or 
rock  dump  without  danger  of  damage  from  falling  pieces  or  from  mine 


140  LOADING  THE  BELT 

props,  tools  and  such  things  which  sometimes  come  in  run-of-mine  coal. 
It  does  not  give  a  uniform  load  on  the  belt  because  it  seldom  makes  over 
30  strokes  a  minute,  but  if  it  delivers  to  the  belt  through  a  long  chute  or 
through  a  crusher,  its  intermittent  or  pulsating  feed  is  made  more  nearly 
uniform.  The  shaker  feeder  (Fig.  130)  is  a  modification  of  Fig.  129;  its 
strokes  are  shorter  and  quicker  and  when  it  loads  a  belt  through  a  short 
chute,  the  load  cross-section  is  apt  to  be  more  uniform. 

No  mechanical  feeder  will  pile  a  perfectly  uniform  load  from  end  to  end  of 
a  fast-moving  belt.  The  rate  of  feet  per  minute  or  even  per  second  may  be 
uniform,  but  the  variation  of  feed  within  a  second  may  be  enough  to  leave 
thin  places  or  bare  places  on  a  belt  traveling  10,  8  or  even  4  feet  per  second. 

The  Stuart  patent  1175190  of  1916  covers  the  idea  of  using  two  or  more 
belt  feeders  in  series  to  deliver  to  a  high-speed  conveyor  belt.  The  first 
feeder  receives  from  a  hopper  or  other  source  of  supply  at  low  speed;  the 
second  feeder  receives  from  the  first,  runs  at  much  higher  speed  and  delivers 
to  the  conveyor  belt. 

Other  Loading  Devices. — Several  throwing  devices  have  been  suggested 
for  delivering  material  to  belt  conveyors  with  a  velocity  that  will  lessen 


0  ®  © 

FIG.  129. — Reciprocating  Plate  Feeder.  FIG.  130. — Shaking  Feeder. 

or  avoid  abrasion  of  the  belt  surface.  In  1912  Thomas  A.  Edison  patented 
a  paddle-wheel  feeder  for  use  with  fixed  belt  trippers  where  it  was  necessary 
to  carry  the  material  past  the  tripper.  It  was  intended  to  remove  the  great 
objection  to  a  series  of  fixed  trippers,  i.e.,  the  wear  on  the  belt  from  repeated 
reloading.  The  scheme  was  tried  once  on  pulverized  cement  and  discarded 
after  a  day's  run.  Similar  methods  are  disclosed  in  the  two  Reinecke  patents 
of  1911.  Neither  of  them  has  come  into  practical  use;  they  are  costly  and 
complicated  and  would  take  up  more  room  than  is  necessary  for  a  good 
chute.  The  cheapest  and  best  way  to  speed  material  up  to  belt  velocity 
is  to  let  the  force  of  gravity  do  it.  There  are,  of  course,  places  where 
chutes  must  be  short,  but  it  is  well  to  remember  that  the  expense  of  making 
a  pit  a  foot  deeper  or  an  elevator  a  foot  higher  is  often  very  much  less  than 
the  continuing  cost  of  the  added  wear  on  the  belt. 

Maxim. — It  may  be  set  down  as  a  maxim  that  the  proper  duty  of  a 
conveyor  belt  is  to  convey,  not  to  speed  up,  material. 

Traveling  Loading  Hoppers. — When  a  belt  draws  its  supply  from  more 
than  one  point,  as  from  a  number  of  openings  under  a  long  bin,  or  from  a 
number  of  bins,  there  is  a  choice  between  using  a  number  of  chutes  or  a 


LOADING  INCLINED  BELT  CONVEYORS 


141 


single  traveling  hopper.  In  handling  grain  it  is  sometimes  possible  to  use  a 
number  of  fixed  chutes,  set  with  some  clearance  over  the  belt  and  with 
a  pair  of  concentrators  (Fig.  27^  at  each  to  prevent  scatter  and  spill; 
but  with  coarser  and  more  abrasive  materials,  fixed  chutes  with  their 
skirt-boards  would  interfere  with  the  flow  of  material  past  them  and  would 
be  apt  to  damage  the  belt.  The  chutes  can  sometimes  be  arranged  to  swing 
clear  of  the  belt  when  not  in  use,  but  it  is  frequently  more  satisfactory  and 
often  less  expensive  to  use  a  traveling  loading  hopper. 

Such  hoppers  for  grain  are  comparatively  light  and  can  be  pushed  by 
hand.  They  consist  of  a  box  or  funnel  mounted  on  four  wheels  which 
travel  on  a  track  to  which  they  can  be  clamped.  The  belt-loading  chute 
is  fixed  at  the  proper  distance  above  the  belt  and  there  are  four  concentrator 
pulleys  carried  on  pivoted  arms  which  by  means  of  a  hand-lever  can  be 
thrown  into  the  operating  position,  or  else  thrown  over  to  clear  the  fixed 
concentrators  of  the  conveyor  when  the  hopper  is  moved. 

Traveling  hoppers  which  draw  coarse  materials  from  bins  are  usually 
fitted  with  a  feeder,  because  ^^_^_^^_^^r_^^===^^__^__^^^_r^^_^( 
whence  bin  gate  is  opened 
wide  it  is  often  impossible  to 
control  the  flow  by  hand  so 
as  to  deliver  a  uniform  load 
to  the  belt.  In  some  cases 
the  traveling  frame  is  pro- 
pelled by  a  motor  which  also 
drives  a  feeder  of  some  kind. 
Fig.  131  shows  a  different 
kind  where  the  conveyor  belt 
furnishes  the  power  for  the 

traveling  hopper.  The  belt  passes  around  two  pulleys  at  the  end  of  the 
frame  as  in  a  tripper,  and  from  a  shaft  driven  by  paper  friction  wheels  on 
one  or  the  other  of  the  pulley  shafts,  power  is  taken  by  chain  drives  to  an 
axle  under  the  frame  and  to  the  head  of  the  apron  conveyor.  A  jaw  clutch 
on  the  latter  allows  the  feeder  to  be  thrown  out  of  gear  during  the  traveling 
motion  (Robb  patent,  1904). 

Loading  Inclined  Belt  Conveyors. — The  slope  of  an  inclined  conveyor  is 
usually  limited  by  the  tendency  of  the  material  to  roll  downhill;  hence, 
screened  or  sized  material  cannot  be  carried  on  angles  as  steep  as  where  the 
lumps  in  a  mixture  rest  on  a  bed  of  fines.  An  intermittent  feed  is  objec- 
tionable when  the  angle  approaches  the  maximum;  single  lumps  fed  to 
the  belt  may  not  be  picked  up  promptly,  but  may  tumble  around  between 
the  skirt-boards  for  a  time  until  a  flat  place  happens  to  rest  on  the  belt. 
The  tail  end  of  an  intermittent  feed  may,  for  lack  of  a  backing,  become 
detached  on  the  incline  and  dance  up  and  down  on  the  belt  until  the  feed 
is  resumed,  or  perhaps  it  may  roll  off.  Conditions  like  these  have  fixed 
the  angles  at  which  it  is  practicable  to  convey  various  materials.  For 
example : 


Conveyor  Belt  Return 


•  of  Tunnel 


FIG.  131.— Traveling  Hopper  with  Feeder  Taking 
Power  from  the  Conveyor  Belt. 


142  LOADING  THE  BELT 

Washed  and  screened  pebbles 12° 

Cushion-shaped  briquettes 12° 

Egg-shaped  briquettes,  less  than 12° 

Clean  anthracite  coal  in  domestic  sizes .  17° 

Crushed  screened  coke 17° 

Run-of-mine  coal,  crushed  stone,  run-of-oven  coke .  .  18° 

Small  crushed  coal 20° 

Bituminous  slack  when  moist 22° 

Tempered  foundry  sand 24° 

Wet  sand 27° 

Fresh  wood  chips 27° 

In  general,  these  angles  are  10°  or  15°  less  than  the  slopes  at  which 
the  material  will  rest  on  the  belt  without  moving.  They  may  be  determined 
by  experiment  with  some  of  the  material  and  a  piece  of  belt,  but  it  is  well  to 
remember  that  when  the  angle  of  incline  approaches  the  maximum  for  any 
material,  there  is  danger  that  the  material  may  at  times  slip.  This  may  be 
due  to  irregular  loading  leaving  bare  places  on  the  belt,  to  difference  in  the 
amount  of  moisture  in  the  material,  or  to  the  depth  of  load  carried. 

The  condition  of  the  belt  surface  also  has  an  effect  on  the  way  it  picks 
up  the  load ;  if  it  is  covered  with  fine  dry  dust,  or  if  it  is  a  new  belt  with  the 
sulphur  "  bloom  "  still  on  it,  or  if  on  a  cold  day  it  is  covered  with  minute 
frost  crystals,  the  material  may  slip  on  it  and  refuse  to  go  up  the  incline. 
Cleaning  off  the  dust  or  getting  rid  of  the  frost  by  sprinkling  salt  on  the 
belt  are  simple  remedies  which  sometimes  cure  the  trouble,  but  sometimes 
the  angle  is  so  steep  that  there  is  nothing  to  do  but  roughen  the  belt  surface 
by  fastening  strips  of  belt  on  it  or  driving  clinch  rivets  through  it.  As  a 
general  rule, — "  better  be  safe  than  sorry  " — keep  the  angle  of  incline  less 
than  the  maximum. 

In  handling  very  gritty  substances  it  is  better  to  keep  the  angle  well 
under  the  maximum  at  which  it  is  possible  to  carry  them  without  roll  or 
visible  slip,  because  in  passing  over  the  idlers  there  is  an  invisible  slip  or 
rearrangement  of  load  which  at  steep  angles  scours  the  face  of  the  belt. 
There  have  been  cases  where  short  steep  belts  handling  gritty  ore  failed 
very  rapidly  from  destruction  of  the  rubber  cover  due  to  this  invisible 
slip  of  material. 

For  economical  speeds  for  inclined  belts,  see  page  154. 

For  loading  chutes  for  inclined  belts,  see  page  141. 

For  skirt-boards  for  inclined  belts,  see  page  137. 

For  belt  pulls  for  inclined  belts,  see  page  113. 

Choosing  a  Safe  Angle  of  Incline. — In  preliminary  layouts  of  inclined 
belts  it  is  well  to  assume  an  angle  safely  under  the  maximum,  then  there 
will  be  some  leeway  to  increase  the  angle  should  it  become  necessary  during 
the  development  of  the  details.  Those  experienced  in  such  matters  knogr 
that  in  the  final  drawings  the  foot  of  an  inclined  conveyor  is  generally  lower 
and  the  head  often  higher  than  in  the  original  plans.  Both  of  these  changes 


CAPACITY  OF  TROUGHED  BELTS  143 

increase  the  angle  of  incline  unless  the  horizontal  distance  between  terminals 
can  be  increased.  It  is  often  incbnvenient  or  perhaps  impossible  to  do  that, 
since  at  slopes  around  18°  or  20°  £iie  foot  of  vertical  height  corresponds  to 
three  feet  of  horizontal  distance  and  to  change  the  height  one  foot  without 
altering  the  angle  means  that  the  terminals  must  be  separated  horizontally 
three  feet  or  more. 

Much  of  the  trouble  with  inclined  belts  comes,  not  from  choosing  the 
wrong  angle  for  the  material  carried,  but  from  the  fact  that  in  the  develop- 
ment of  the  plans,  the  angle  becomes  steeper  than  was  at  first  intended. 

Change  in  Practice. — In  the  early  days  of  belt  conveying  some  engineers 
used  angles  of  slope  up  to  6  in  12  (26^°)  in  order  to  use  short  conveyors  or 
avoid  the  use  of  elevators.  Sometimes  the  conditions  of  feed  and  of  the 
material,  crushed  coal,  crushed  rock,  etc.,  etc.,  were  such  that  the  conveyor 
worked  satisfactorily,  but  more  often  there  were  difficulties  and  disappoint- 
ments. In  recent  times  practice  has  changed  and  angles  over  20°  are  now 
rare. 

Special  Belts  for  Inclined  Conveyors. — Robins  in  1906  patented  (810510) 
a  rubber  belt  "  provided  upon  its  carrying  surface  with  marginal  and  trans- 
verse elevations  of  the  same  height."  The  elevations,  acting  as  rubber 
cleats,  prevented  the  material  from  slipping  on  the  belt  and  made  it  possible 
to  run  the  conveyor  at  an  angle  steeper  than  ordinary.  The  marginal 
elevation  allowed  the  belt  to  run  over  a  snub  pulley  or  the  return  idlers 
without  bumping,  but  the  whole  construction  was  costly  and  it  was  not  used 
more  than  once  or  twice.  Fine  material  would  lodge  in  the  corners  on  the 
carrying  surface  of  such  a  belt,  and  since  a  brush  could  not  clean  it  well, 
there  would  be  more  drip  on  the  return  run  than  with  a  smooth  belt. 

Norton  in  1907  patented  a  tailings  stacker  belt  (see  p.  19)  in  which 
the  cleats  or  ribs  are  thick  in  the  middle  of  the  belt  and  do  not  extend  to  the 
edges  of  the  belt. 

Capacity  of  Belts  as  Affected  by  Troughing. — In  1896  Robins  published 
a  table  of  capacities  of  belts  troughed 
at  45°  in  which  cubic  feet  of  material 
per  hour  at  100  feet  per  minute  belt 
speed  =  1.3TF2  where  W  =  width  of  belt 
in  inches.  Fig.  132  shows  to  scale 

what  the  effective  load  cross-section,   _, 

-•    FIG.   132. — Load  Cross-section   According 
according    to    that    table,  looks  like  to  Capacity  Rating,  1896. 

on  the  belt.     It  is  probable  that  the 

rating  was  based  on  some  actual  records  but  tempered  by  caution  lest 

inexperienced  operators  might  expect  too  much  from  their  belts. 

In  modern  practice  capacities  are  rated  higher.  One  formula  used  by 
Robins  and  others  for  belts  on  three-pulley  or  five-pulley  idlers  is  cubic 
feet  per  hour  at  100  feet  per  minute  =3.2W 2;  Jeffrey  uses  3.5 TF2;  Stephens- 
Adamson  Co.,  3PF2;  Link-Belt  Co.  uses  a  graduated  formula  in  which 
the  factor  varies  from  2.8  for  12-inch  belt  to  3.3  for  54-inch  belt.  These 
capacities  can  be  expressed  as  square  inches  of  load  cross-section  carried 


Belt  Capacity  based  on  this  load 
Cu.Ft.per  Hr@l<»  ft.p.m.  = 
Effective  Depth  X  =  .08W 


144 


LOADING  THE  BELT 


on  the  belt;  they  are  shown  in  Figs.  133,  134,  135,  136  drawn  to  scale.  In 
every  case  the  effective  cross-sections  represent  much  less  than  what 
might  be  piled  at  a  slope  of  4  in  10  (about  22°)  with  the  lower  edges  of  the 


n 
r -width  of   C 

Belt,  inches 


E 
FIG.  133. 


W  -Width  of  Celt,  inches* 

FIG.  133. 


FIG.  134. 


Capacity  of  belt  on  5-pulley  idlers  based  on  3.2 W*  (Robins). 

Depth  of  pile  Y  sloped  4  in  10         =  .205  W. 

Depth  X  of  equivalent  flat  load  =  .  129  W. 

For  3-pulley  idlers  troughed  30°,  Y  =  .19TF;  X  =  .135TF. 

For  explanation  of  ABODE,  see  page  82. 

FIG.  134. 

Capacity  of  belt  on  3-pulley  idlers,  based  on  3.5TF2  (Jeffrey). 
Depth  of   pile   Y  sloped  4   in    10  =  .21QW. 
Depth   X   of  equivalent  flat  load  =  .  144  W. 

pile  a  few  inches  from  the  edge  of  the  belt.  The  slope  of  4  in  10  in  these 
figures  is  assumed  as  representing  an  angle  less  than  the  angle  of  repose  of 
most  materials  when  stationary,  and  as  an  approximation  to  the  shape  of 
the  average  pile  with  the  belt  in  motion.  Shown  as  loads  with  a  flat  top, 


FIG.  135. 


FIG.  136. 


FIG.  135. 


Capacity  of  belt  on  3-pulley  idlers,  based  on  3TF*  (Stephens-Adamson). 
Depth  of  pile  Y  sloped  4  in  10     =  .19TF. 
Depth  X  of  equivalent  flat  load  =  .HTF. 

FIG.  136. 

Capacity  of  belt  on  3-pulley  idlers  with  wide  center-pulley  based  on  3W*  (Main  Belting 
Co.). 

Depth  of  pile  Y  sloped  4  in  10     =  .18W. 
Depth  X  of  equivalent  flat  load  =  .094  W. 

the  level  of  the  top  would  in  every  case  (except  Fig.  136)  come  below  the 
line  joining  the  edges  of  the  belt  in  the  troughed   position.     On  the  five- 
pulley  idler  the  greatest  possible  load 
piled  at  4  in  10  is  about  double  the 
rated  load  (see  Fig.  137).     It  might 
be  attained  if  the  belt  speed  were  low, 
the  conveyor  level,  and  if  the  ma- 
terial, free  from  large  lumps,  were 
carefully   fed   to   the   belt   through 
a    wide   chute.      This    combination 
FIG.  137.— Comparison  between  Normal  Load    of    conditions    seldom    occurs;     the 
and  Maximum  Load  on  3-pulley  or  5-pul-  ,        r  •   ,  .      ,-,      e      •,     i 

ley  Idlers.  supply  of  material  to  the  feed  chute 

or  to  the  automatic  feeder  is  sel- 
dom exactly  uniform;   the   speed  of   the   belt  in   relation   to   the  feed  is 


.  VOutline  of  3  pulley 
idler 


CAPACITY  AS  AFFECTED  BY  OPERATING  CONDITIONS      145 

often  such  that  the  load  on  the  belt  is  not  even  and  some  parts  may 
receive  no  load  at  all.  Belts  "cannot  be  fed  through  a  chute  wider  than 
%W  for  fear  of  material  scatteringssideways  or  lumps  rolling  off  the  belt  even 
where  skirt-boards  are' used  at  the  loading  point.  Again,  on  inclined 
conveyors,  the  agitation  of  the  load  in  passing  over  idlers  causes  the  peak 
of  the  pile  to  sink,  and  the  pile  assumes  an  angle  of  slope  flatter  than  the 
one  it  assumes  on  a  level  run.  The  ratings  adopted  by  manufacturers  of 
conveying  machinery  and  makers  of  belts  are  suited  to  average  practice  for 
belts  horizontal  or  at  angles  of  20°  or  less;  they  cover  the  ordinary  con- 
tingencies met  with  in  operating  conveyors.  In  some  cases  where  the 
loading  cannot  be  controlled  with  uniformity,  or  where  fine  lively  material 
like  cement  is  carried  on  an  inclined  conveyor,  it  is  wise  to  expect  capacities 
even  lower  than  those  given  by  standard  formulas.  One  corporation  that 
operated  a  coke  and  gas  plant  in  the  West  used  the  following  rule:  "  To 
find  the  capacity  of  a  conveyor  belt,  make  a  diagram  of  the  troughing  idler, 
measure  2  inches  down  from  the  edges  of  the  belt,  draw  a  straight  line  across, 
calculate  the  area  between  it  and  the  belt  and  from  it  the  number  of  tons 
according  to  the  material  handled  and  the  belt  speed.  Then  discount  this 
one-third  and  the  result  will  approach  the  average  maximum  that  one  will 
get  in  practice." ,  For  a  standard  five-pulley  idler,  this  rule  comes  to 
cubic  feet  per  hour  at  100  feet  per  minute  =2W2.  It  was  based  on  long 
experience  in  handling  run-of-mine  coal,  crushed  coal  and  coke  on  many 
belts,  some  level,  but  mostly  inclined  at  angles  between  15°  and  20°.  It  is 
a  rule  that  is  not  recommended  for  general  practice,  but  it  is  quoted  to 
emphasize  the  fact  that  there  are  conditions  where  the  ordinary  safe  rule 
cubic  feet  per  hour  at  100  feet  per  minute  =3.2W2  gives  results  not  attainable 
in  practice. 

Capacity  as  Affected  by  Operating  Conditions. — The  factors  which  lower 
the  capacity  of  a  belt  conveyor  are  generally  external  to  the  belt,  such  as 
delay  in  placing  coal  cars  over  the  dump,  delay  in  removing  empty  cars, 
trouble  in  getting  coal  out  of  the  cars,  trouble  with  crushers,  delay  in 
changing  position  of  trippers,  screens  clogging,  chutes  filling  up.  stopping 
for  lubrication  or  machinery  troubles.  All  these  reduce  the  time  of  actual 
conveying;  experienced  engineers  always  make  some  allowance  for  them 
and  choose  a  belt  wide  enough  to  give  the  required  capacity  during  the  net 
working  time. 

The  factors  mentioned  above  are  often  more  important  in  fixing  the 
capacity  of  a  conveyor  than  the  amount  of  troughing  the  belt  receives. 
It  can  be  shown  that  for  a  given  angle  representing  the  way  a  certain 
material  piles  on  the  belt  there  is  an  angle  of  setting  the  troughing  idlers 
which  for  a  belt  loaded  to  its  edges  gives  the  maximum  cross-section,  and 
hence  the  greatest  belt  capacity.  For  crushed  coal,  this  angle  is  not  far 
from  30°  on  three-pulley  idlers,  but  whether  the  idlers  are  set  at 
20°  or  35°,  these  full  cross-sections  are  not  very  different  from  the  theoretical 
maximum  at  30°,  and,  as  may  be  seen  from  the  figures,  the  ordinary  safe 
ratings  derived  from  practice  are  much  lower  on  any  idler  than  would  be 


146 


LOADING  THE  BELT 


represented  by  the  full  cross-sections.  Then,  as  has  been  said,  the  piling 
of  the  material  on  the  belt  varies  with  the  nature  of  the  material,  the 
width  of  the  feed  chute  and  the  angle  of  incline;  taking  all  these  things 
into  consideration,  it  is  not  worth  while  to  make  rules  which  base  carrying 
capacity  on  small  variations  in  the  angle  of  troughing.  The  ratings  which 
are  published  by  various  engineering  firms  and  which  are  shown  in  Figs. 
133  to  136  inclusive,  are  in  all  cases  lower  than  capacities  at  the  fullest 
loading  of  the  belts.  The  margins  of  safety  are  liberal  and  will  allow  some 
increase  where  the  conditions  are  favorable  for  full  loading  and  steady 
running.  Unless  the  conditions  are  distinctly  abnormal,  it  is  wise  to  use 
the  established  rules  and  if  it  should  appear  in  service  that  the  material 
could  be  piled  deeper  on  the  belt,  the  belt  speed  can  be  reduced  to  what 
will  give  a  good  cross-section  of  load. 

Table  26  gives  carrying  capacities  of  troughed  belts  based  on  cubic 
feet  per  hour  at  100  feet  per  minute  belt  speed  =3.2W2. 

Capacity  of  Belts  Not  Troughed. — If  a  belt  of  width  W  is  run  on  flat 
idlers  without  troughing  and  is  loaded  to  a  distance  of  .13W  from  each 
edge  with  material  that  piles  at  a  slope  of  4  in  10  (22°),  it  will  hold  just 
half  the  maximum  capacity  of  a  belt  troughed  as  shown  in  Fig.  137.  Since 
the  ordinary  safe  rating  of  troughed  belts  is  50  per  cent  of  the  maximum 
possible  loading  (see  Fig.  137)  it  is  proper  to  rate  flat  belts  by  the  same  pro- 
portion of  their  maximum  loading.  Hence,  capacity  of  flat  belts  in  cubic 
feet  per  hour  at  100  feet  per  minute  =1.6  W2. 

In  Fig.  138  the  outer  line  represents  the  maximum  possible  loading  and 


JUxImumload 
Safe  Load- 1.6  W2S 


il 


aximum  Loao  .  8.2W8 
Safe  Load  -  1.6^3 


Maximum  Load- 
Feasible  Load  -  2.5  W? 


lmumLoad-4Wa 
Load~2W-2 


FIG.  138. — Comparison  between  Normal 
Load  and  Maximum  Load  on  Flat 
Belt. 


FIG.  139. — Comparison  between  Normal 
Load  and  Maximum  Load,  Belt  on 
Flared  Idlers. 


the  inner  lines  are  the  slopes  of  piles  that  hold  half  as  much.  These  slopes 
are  shown  12°  (2  in  10)  and  22°  (4  in  10)  and  edges  of  the  piles  are  A5W 
or  more  away  from  the  edge  of  the  belt. 

For  capacities  of  flat  belts  of  various  widths,  take  one-half  the  values 
given  in  Table  26. 

Capacity  of  Belts  on  Flared  Idlers. — If  a  belt  on  Uniroll  or  commercial 
flared  idlers  (see  Chapter  IV)  is  loaded  to  within  1  inch  of  the  edges  of 
the  belt  with  material  that  piles  at  4  in  10,  it  will  hold  five-eighths  as  much 
as  the  maximum  loading  of  a  belt  troughed  as  shown  in  Fig.  147.  Keeping 
the  same  ratio  between  safe  loading  and  maximum  loading  as  for  troughed 
belts,  we  get  the  rule:  capacity  of  belts  on  Uniroll  idlers,  cubic  feet  per 
hour  at  100  feet  per  minute  =2TF2. 

The  right  half  of  Fig.  139  shows  by  the  outer  line  the  maximum  possible 
loading  of  such  a  belt  on  the  basis  stated  above;  the  inner  lines  are  the 


CAPACITY  OF  BELTS  BASED  ON  3.2  TF2 
83$££ 

fc 


147 


*°S 
&& 

>>43 


a  o 

62 


II 

o2 


PQ 


B 


•§•3 


*I-i* 


iofl 
^  «5 


i—  (O500O<Nt>- 


COOSOOO^'-H 


OC^^OGOOCOtOOOOCO 
T-II—  li—  ii—iT-iC'lC<l(NC^CCCC 


(N(NOOOCX)(M(M 


OCX)(M(MOO 
OO'-i!-iOOO5 


C^  <M  <N  <N 


(N(NGOOO«OOOOOO 


OO«OOOO 
r-i^^CC05(M 


CO  1-1  ^  CO 

OT^OOClOO5 
t^O»OCO(N 
CO  *O  ^O  00  O 


^ 


S't^O5 
(Ni-H 


148  LOADING  THE  BELT 

slopes  of  piles  that  hold  one-half  the  maximum.  These  safe  load  cross- 
sections  are  shown  with  slopes  of  12°  and  22°;  all  of  them,  12°  or  steeper, 
come  well  away  from  the  edges  of  the  belt. 

If  the  conveyor  is  not  inclined  at  more  than  10°  from  the  horizontal 
and  if  the  loading  is  uniform  it  is  possible  to  carry  more  than  2W2  over  flared 
idlers.  The  left  half  of  Fig.  139  shows  safe  load  cross-sections  one-fourth 
greater  than  those  on  the  right  half.  For  these  conditions,  cubic  feet  per 
hour  at  100  feet  per  minute  =  2.5T72. 

Table  27  gives  capacities  of  belts  in  cubic  feet  per  hour  at  100  feet 
per  minute  for  2W2,  2.5TF2  and  other  ratings  based  on  various  belt  loadings. 

Capacity  of  Inclined  Belts. — When  the  angle  of  the  conveyor  does  not 
exceed  20°  the  safe  carrying  capacity  of  belts  may  be  taken  the  same  as 
for  horizontal  conveyors;  but  since  the  material  on  the  incline  tends  to 
assume  a  flatter  slope  than  on  the  level  as  seen  in  cross-section  there  is  not 
in  inclined  conveyors  the  same  margin  between  the  maximum  possible 
capacity  and  the  capacity  as  given  by  the  ordinary  rule,  cubic  feet  per  hour 
at  100  feet  per  minute  =3.2TF2. 

For  that  reason  and  because  it  is  harder  to  load  inclined  belts  the  capacity 
seldom  if  ever  exceeds  that  given  by  the  usual  rule. 

In  estimating  carrying  capacities  for  inclined  conveyors  consideration 
should  be  given  to  the  fact  that  belt  speeds  should  sometimes  be  less  than 
those  for  horizontal  conveyors  (see  Table  30,  p.  154). 

Hourly  Capacities. — For  material  like  coal,  which  weighs  about  50 
pounds  per  cubic  foot,  the  ordinary  rule,  cubic  feet  per  hour  at  100  feet 
per  minute  =  3.2TF2,  becomes:  tons  of  coal  per  hour  =  .08 If2  at  100  feet 
per  minute,  or  8  per  cent  of  the  square  of  the  width  of  the  belt  for  every 
100  feet  of  belt  speed.  Ton  here  means  short  ton  of  2000  pounds. 

Peak  Load  Capacities. — All  rules  for  belt  capacity  apply  to  average 
conditions  of  loading  where  the  feed  is  fairly  uniform;  but  where  a  feeding 
device  cannot  be  used  or  where  the  belt  takes  from  a  machine  like  a  crusher 
whose  rate  of  output  for  a  period  of  some  minutes  may  greatly  exceed  its 
average  hourly  rate,  then  the  capacity  of  the  belt  should  be  considered  on 
the  minute  basis  and  not  the  hour  basis,  unless  the  chute  or  hopper  under 
the  crusher  is  large  enough  to  hold  the  excess  of  material  during  the  time 
when  the  crusher  output  is  above  the  hourly  rate.  (For  an  example  based 
on  this  condition,  see  p.  116.) 

An  excess  of  belt  capacity  over  the  average  hourly  rate  should  also  be 
provided  where  the  conveyor  receives  material  dug  from  cars  or  boats  by  a 
grab-bucket.  When  unloading  begins  from  a  full  car  or  boat,  digging  is 
easy  and  the  bucket  will  bring  up  more  rapidly  than  later  when  the  material 
gets  low  and  the  bucket  cannot  dig  so  well  nor  be  handled  so  fast.  In 
cases  of  this  kind  the  output  at  first  may  greatly  exceed  the  hourly 
average. 

There  are  also  conditions  which,  in  order  to  maintain  a  certain  daily 
total,  require  conveyors  to  handle  per  minute  or  per  hour  loads  much 
greater  than  average.  These  are  frequently  overlooked  in  discussing  the 


CAPACITIES  AT  VARIOUS  RATINGS 


149 


p 


pf]  pt( 

6s 


O  rt*  O  (N 

rH  CO  Q  CO 


C<l  CO  l>  O  ^ 

b-    rH    CS   O   CO    rH   t>.    T^  O   l>_  ^  <N   CD_  ^  CO 

cQ-*&-*£u$if5(Dt*~t*~<xo)r-4-*£<o 


iOt>Ci<NiOXrHiOO5COXCOX^fOCO<N 


O 


COCOCOiOOt^r^O5Tt<<N<MiO'H 
•*COXOCOiOXrHioaiCOl><N 


COiMrHCOCC^^cOOOOt^O-^iMC^^Ot^t^COIN 

ThCOCOO(N>OCOrHlOGOC^t>rHCOrHCDrHt>.COCOtO 


COOiCOOiI^-CO'-Hl>COcDOiO^ti^t| 
t^»  O  "^  t^»  i~^  *O  O  Tt^  O5  ^  O  iO  i~^  O 

i-T  c^  oj  ci"  co"  co"  •*"  -^f  rf  uf  o"  o  i>  cT 


(M  CO  CO  (N 

CO  CO  CD  t^ 

Tt<    IO   1>    O5 


XCOCqOC^COCOiMO(NXGO(NCO 
(N(MiOOI>CDCOCOOOlCO^rHTf< 
l>OCOt>OT^COCOCO<NCOCOOiI> 


rHrHrHrH<N<N<MCOCO'*T*lO*OCOCOOCOrH 


I-H  r-    C     C<    C<    CO  CO  CO  •*  -^  10  iO  CO  CO  o    I-H 


cDOi'*i-iOi-H 


-<t'-(O'-H 
C<|COC5^ 

<N  cq  <N  co"  co"  "<*"•*" 


CDO5Or^ 
t^(NO(N 

"f  i>"  oT  o" 


rHCOOiOO>CDrHTt<l— lOCD 
OrH^OCOlOCOXCDOrH 


(N(NCOOCO<M(MGO 


C^    CO    »O   CO   GO    O5    rH 


OCO<M 

O-^rH 


(M  CSJ  CO  <N 

X  <M  CO  CO 


<M  CO  X  t^  O  l> 
<M  CO  ^  »O  b-  X 


X  X  O  CO  O  O  CD 
rt<  »O  CO  b- 


££      —      —     ^     ^     ^0 

rHO5XXO<NCDrH 

<NC^CO-^«Dl>XO 


XOirH^XC^XlOCO<NrH(NCOCDO5(NrH 

lOcOXOiOfMCOiOt^OirHfO'O^'^coOi 

CO  Tt< 


•^CDCOTtHO-^CDCOTt* 

Tf<O5iO(MOXt^l>X 

rHrH<MCO^-*»OCDt^ 


T}H  CO  CO  Tf<  CO  O  CO 

t>«   Ol    rH    CO   OS    CO   O 


<N  TJH  CO  X  O  <N 

rH    rH    1-1    rH   (N    (N 


H?-» 

X 


-rtl°  x 


§  * 

>»   13     a 

1*1 

1  -i    fi 

"I  I 

X2       ^, 

1    3    3 


&    H    E^ 


150 


LOADING  THE  BELT 


capacity  of  the  conveyor.     The  capacity  should  of  course  be  equal  to  the 
"  peak  load  "  and  not  to  the  average  rate. 

Capacities  of  Grain  Belts. — The  last  half  of  Fig.  140  shows,  to  scale, 
the  load  cross-sections  corresponding  to  belt  capacities  as  given  by  three 
authorities.  Rule  No.  3,  bushels  per  hour  at  100  feet  per  minute  =  1.75 W2, 
used  by  the  Webster  Manufacturing  Co.,  represents  what  a  belt  with  con- 
centrators will  carry  under  average  conditions  of  loading  from  a  single 


Width  of  Belt 
W=  in  inches 


Troughed  Belt  Flat  Belt 

FIG.  140. — Capacities  of  Grain  Belts  According  to  Several  Rules. 

Rule  1. — Bushels  per  hour  at  100  feet  per  minute  =  2.5TF2. 
2. — Bushels  per  hour  at  100  feet  per  minute  =  2.2  W*. 
3. — Bushels  per  hour  at  100  feet  per  minute  =  1.75PF2. 

W 
For  flat  belts  where  width  of  chute  =  —. 

Bushels  per  hour  at  100  ft.  per  min.  =  1.2PF2. 


spout.  When  the  concentrators  come  every  10  or  12  feet  some  additional 
load  can  be  added  by  a  second  or  a  third  spout  without  spill  over  the  edges 
of  the  belt.  There  is  no  accepted  rule  for  what  may  be  added  in  this  way, 
but  the  increase  may  be  as  much  as  40  per  cent  without  exceeding  the 
loading  shown  by  line  1,  which  represents  the  rule  of  H.  W.  Caldwell  &  Sons 
Co.,  i.e.,  bushels  per  hour  at  100  feet  per  minute=2.5TF2.  The  load  of 

grain  carried  by  a  fast-moving  belt 
has  a  top  which  is  nearly  flat;  the 
lines  1,  2,  3,  therefore,  show  about 
what  the  loads  look  like  according 
to  the  three  rules. 

The  angle  of  the  concentrators 
(Fig.  27)  has  very  little  effect  on  the 
load  cross-section  in  the  diagram; 
steep  concentrators  with  60°  angle 
are  sometimes  used  where  a  belt  is 
fed  simultaneously  from  a  number 
of  spouts  or  from  a  continuous 


FIG.  141. — 40-inch  Belt  with  Continuous 
Loading  Trough  and  60°  Concentrators, 
Public  Grain  Elevator,  New  Orleans 
(Ford,  Bacon  &  Davis,  Engrs.) 


loading  channel  under  a  track  pit 
(Fig.  141).  Here  the  steep  upturn 
of  the  edges  of  the  belt  prevents 
the  grain  from  scattering  sideways 

as  it  hits  the  belt.  Usually  the  angle  is  45°  or  less;  35°  is  common, 
but  30°  and  even  22°  angles  are  in  use.  There  is  no  doubt  that  the  flatter 
the  angle,  the  easier  the  action  on  the  belt. 


SPEEDS  OF  BELT  CONVEYORS 


151 


Grain  belts  narrower  than  20  -inches  in  4-ply  or  even  3-ply  thickness 
are  relatively  stiffer  than  wider  belts  in  the  usual  4-ply  thickness,  and  show 
more  tendency  to  flatten  out  between  the  concentrators.  To  get  the 
rated  capacities  it  is  necessary  to  feed  them  with  greater  care  and  to  keep  a 
concentrator  at  each  feed  spout;  and  it  is  not  usually  possible  to  increase 
the  rated  capacity  by  feeding  from  a  second  or  a  third  spout.  Experienced 
grain-elevator  engineers  recognize  these  difficulties  with  narrow  belts  and 
do  not  use  them  at  their  published  ratings,  even  the  low  ratings. 

The  right  half  of  Fig.  140  shows  the  loading  of  a  flat  belt  without  con- 
centrators, where  the  mouth  of  the  spout  is  about  half  the  width  of  the 

W 
belt.     With  a  clear  margin  on  each  side  of  —  ,  the  capacity  of  the  belt  in 


bushels  per  hour  at  100  feet  per  minute  = 

Table  28  gives,  in  form  for  comparison,  capacities  of  grain  belts  with 
concentrators  as  rated  by  four  authorities.  The  ratings  suggested  by 
the  author  in  the  sixth  column  are  lower  than  any  of  the  others  for  the 
narrow  belts. 

TABLE  28.—  CAPACITIES  OF  GRAIN  BELTS  WITH  CONCENTRATORS 


Bushels  per  Hour  at  100  Feet  per  Minute 

Advisable 

C»      J 

Belt 
Width, 
Inches 

Caldwell, 
Line  1 
in  Figure 

Goodrich, 
Line  2 
in  Figure 

Webster, 
Line  3 
in  Figure 

Weller 

Safe  Rule  for 
Usual  Conditions 
of  Feed 

Speeds, 
Feet 
per 
Minute 

12 

368 

290 

253 

192 

200 

300 

14 

505 

430 

346 

344 

300 

350 

16 

655 

580 

453 

500 

400 

400 

18 

832 

740 

570 

652 

550 

450 

20 

1025 

910 

706 

800 

700 

500 

22 

1240 

1090 

866 

960 

860 

600 

24 

1480 

1280 

1027 

1096 

1020 

600 

26 

1745 

1480 

1200 

1280 

1200 

600 

28 

2000 

1680 

1400 

1456 

1400 

600 

30 

2320 

1900 

1600 

1660 

1600 

650 

32 

2640 

2140 

1826 

1860 

1826 

650 

34 

2960 

2400 

2053 

2053 

650 

36 

3360 

2650 

2333 

2304 

2333 

700 

38 

3680 

2560 

2560 

700 

40 

2800 

2800 

2800 

700 

42 

4480 

3120 

3080 

3120 

750 

44 

4960 

3400 

3400 

750 

46 

3790 

3790 

750 

48 

5920 

4070 

3960 

4070 

800 

Speeds  of  Belt  Conveyors. — The  great  advantage  of  belt  conveyors 
over  other  forms  of  continuous  conveyors  is  that  they  can  run  at  higher 
speeds  without  increase  of  noise  or  much  greater  friction  losses.  So  far  as 
the  transfer  of  material  is  concerned,  all  belt  conveyors  could,  like  grain 
conveyors,  be  run  up  to  the  speed  at  which  the  material  would  be  blown  off 
the  belt  by  the  resistance  of  the  air.  In  practice,  however,  other  factors 


152  LOADING  THE  BELT 

govern  the  speed.  The  width  of  the  belt  and  its  speed  are,  of  course,  deter- 
mined primarily  by  the  capacity  required;  but,  in  addition,  the  weight, 
size  and  nature  of  the  material  must  be  considered.  If  it  is  easily  broken, 
like  coke  or  anthracite  coal  or  briquettes,  the  speed  must  not  be  so  high  as  to 
discharge  the  material  with  violence  at  trippers  or  at  end  chutes.  (For 
illustrations  of  end  discharge,  see  p.  157.)  If  the  material  is  not  lumpy  or 
abrasive,  especially  when  it  is  free-flowing  like  grain  or  crushed  coal,  and  the 
supply  is  regular,  as  from  a  large  bin,  the  belt  may  be  run  fast.  Then  the 
loading  chute  can  be  arranged  to  deliver  a  uniform  load  to  a  fast-moving 
belt,  but  it  is  not  economy  to  run  a  belt  fast  and  have  it  only  partly  loaded 
as  must  happen  if  the  material  is  lumpy;  even  though  a  feeder  is  used.  A 
feeder  of  the  apron  or  belt  type  (see  p.  139)  will  deliver  uniform  quantities 
of  material  per  minute,  but  in  working  on  lumpy  or  mixed  material,  the 
fall  of  the  material  over  the  head  of  the  feeder  may  vary  from  second  to 
second,  and  on  a  belt  moving  5  to  10  feet  a  second,  it  is  often  impossible  to 
avoid  a  thin  load  or  even  bare  spots  at  intervals  on  the  belt. 

Full  Load  Cross-section  Desirable. — The  aim  should  be  to  run  the  belt 
no  faster  than  is  necessary  to  give  the  capacity  under  the  conditions  of 
loading.  A  full  cross-section  of  load  at  a  slow  speed  means  a  deeper  pile 
and  proportionately  less  material  in  contact  with  the  belt,  hence  less  cutting 
and  abrasion,  less  strain  from  pick-up  of  material  (see  p.  123)  and  less 
energy  wasted  in  revolving  shafting  and  gearing,  foot 
shafts,  snub  shafts,  tripper  mechanism,  etc.  Fig.  142 
shows  a  belt  carrying  only  one-third  of  its  normal  rated 
load,  and  superimposed  upon  the  light  }oad,  the  other 

FIG.    142.— Compari-    two-thirds  of  its  normal  load.     Only  a  portion  of  the 
son    of    Full  Load         ,  ,    ,    ,       ,     .         ,          ,,        ,    ,.         .    ".       ,,        .,       ,       ,    . 
Capacity  and  One-    added   load   touches   the   belt.     Actually   the  load  is 

third  Capacity.          tripled  with  an  increase  of  60  per  cent  in  the  amount 

of  belt  surface  in  contact  with  the  material.     The  full 

load  distributes  the  load  over  more  of  the  belt,  the  light  load  concentrates 

it  in  the  middle;   and  when  a  belt  is  worn  out  in  the  middle,  it  is  all  worn 

out. 

The  rated  capacities  of  belts  are,  as  may  be  seen  from  Figs.  133  to 
137  inclusive,  considerably  less  than  what  may  be  piled  on  the  belt;  in  some 
cases  where  the  feeding  arrangements  are  favorable,  it  is  possible  to  get  a 
larger  load  cross-section  than  standard  and  hence  a  slower  speed  for  the 
required  capacity.  After  a  belt  conveyor  has  been  in  regular  service  for  a 
short  time  it  is  always  advisable  to  study  the  feed  and  the  load,  and  then 
reduce  the  belt  speed  when  it  can  safely  be  done. 

High  Speeds  not  Practicable  for  Narrow  Belts. — Wide  belts  can  be  run 
faster  than  narrow  belts  because  the  wider  the  belt,  the  deeper  the  load 
and  the  less  material  proportionately  comes  in  contact  with  the  belt  surface 
to  cut  or  abrade  it.  On  a  narrow  belt,  a  greater  proportion  of  pieces  touch 
the  belt  surfaces,  hence,  to  lessen  the  injury  to  the  belt,  its  speed  should  be 
less.  Expressed  mathematically,  belt  capacity  for  a  given  speed  varies 
with  W 2  while  the  belt  surface  passing  the  feed  chute  varies  with  W ;  the 


SPEED  LIMITED  BY  CONSTRUCTION  OF  IDLERS 


153 


ratio  which  measures  the  durability  of  the  belt  under  the  abrasion  of  material 

W2  »   " 

is,  therefore.  —  =  W.     Reasoning  from  this,  a  fully  loaded  48-inch  belt 
W  & 

at  900  feet  per  minute  might  suffer  no  more  than  a  16-inch  belt  at  300  feet 
per  minute  in  handling  the  same  kind  of  material;  but  since  wide  belts  are 
often  chosen  because  they  will  handle  large  lumpy  material  the  speed  for 
wider  belts  is  held  down  to  reduce  the  damage  from  cutting  at  the  loading 
point. 

TABLE  29.— MAXIMUM  ADVISABLE  SPEEDS  FOR  BELT  CONVEYORS 
FOR  COAL,  ORE,  GRAVEL,  ETC. 


Belt  width,  inches  

12 

14 

16 

18 

20 

24 

30 

36 

42 

48 

Belt  speed,  feet  per  minute. 

300 

300 

300 

350 

350 

400 

450 

500 

550 

600 

Table  29  gives  maximum  speeds  for  belt  conveyors  according  to  the 
considerations  mentioned  above. 

Speed  Limited  by  Construction  of  Idlers. — The  pulleys  of  commercial 
grease-lubricated  idlers  revolve  about  60  to  75  r.p.m.  for  each  100  feet  per 
minute  of  belt  travel.  The  pulleys  are  not  centered  and  balanced  as 
transmission  pulleys  are,  and  at  speeds  over  400  or  500  feet  per  minute 
they  are  apt  to  be  noisy  and  the  idler  stands  shake  loose  from  the  vibra- 
tion. For  high  speeds,  the  stands  and  pulleys  of  cast-iron  grease-lubricated 
idlers  must  be  better  than  the  ordinary  kind,  in  some  of  which  the  pul- 
leys are  not  turned  true. 

Possible  Maximum  Speeds. — It  is  probable  that  in  the  future,  belt 
conveyors  for  high  capacity  will  be  equipped  with  improved  feeders  and 
with  ball-bearing  or  roller-bearing  idlers  that  can  run  at  high  speeds.  It- 
may  be  possible  then  to  run  such  belts  almost  up  to  the  speed  at  which 
air  resistance  will  blow  the  material  off  the  belt. 

Minimum  Speeds. — As  may  be  seen  from  Fig.  144,  a  speed  of  140  feet 
per  minute  is  sufficient  to  deliver  material  into  a  chute  set  just  below  and 
under  the  middle  of  the  discharge  pulley.  Since  tripper  chutes  and  end- 
discharge  chutes  are  generally  set  in  that  way,  it  is  not  necessary,  so  far 
as  clean  delivery  of  ordinary  material  is  concerned,  to  run  belts  any  faster 
than  140  feet  per  minute. 

Jeffrey  says,  "  Under  150  feet  per  minute  speed,  the  cost  of  the  belt 
conveyor  per  ton  of  bulk  materials  handled,  even  with  a  minimum  ply  of 
belt,  commences  to  be  uneconomical  as  compared  with  other  types  of 
conveyors  equally  suited  to  the  operating  conditions."  Although  this 
expresses  a  correct  relation  between  belt  conveyors  and  other  types  of 
conveyors  as  to  first  cost  and  operating  cost,  there  may  be  reasons  more 
important  than  costs  which  make  a  belt  conveyor,  at  100  or  150  feet  per 
minute  preferable  to  any  other  conveyor  at  any  speed. 

Short  Belts. — When  belts  are  very  short  each  foot  of  surface  passes  the 
loading  point  frequently,  and  hence  the  wear  is  proportionately  greater 


154 


LOADING  THE  BELT 


than  in  a  long  belt.  For  that  reason  a  short  belt  should  not  be  run  faster 
than  is  actually  necessary. 

Speeds  for  Inclined  Belts. — From  what  is  said  on  page  134  about  loading 
chutes  it  is  clear  that  when  belts  are  loaded  on  an  incline  the  cutting  and 
abrasion  are  likely  to  be  greater  unless  the  angle  of  the  chute  is  flattened 
so  as  to  deliver  the  material  more  nearly  in  the  direction  of  belt  travel. 
It  is  not  usually  possible  to  flatten  the  chute  without  risk  of  choking  it, 
and,  in  addition,  the  flatter  angle  means  less  velocity  of  flow.     Excessive 
wear  on  the  belt  from  sharp  or  abrasive  materials  can  be  avoided  by  run- 
ning the  belt  slower.     In  Fig.  143  if 
the    chute  is  at  angle  of  40°,    which 
represents  a   fair   average,   the   best 
speed  for  material  in  it  is  V  secant  40° 
when  the  velocity  of  the  belt  it  feeds 
is  V  on  the  horizontal.     If  the  belt 
is  inclined  at  an  angle  A  and  runs  at 
a  speed  S,   then  for  the  best  delivery 
of    material  flowing  from  the  chute, 
S  should  equal   V  secant  40°  cosine 
(40°  +  A).     Table  30  has  been  calcu- 
lated on  this  basis;    it  shows  that  if 

for  a  certain  material  it  is  proper  to  run  a  horizontal  conveyor  at  400  feet 
per  minute,  to  handle  the  same  material  on  a  belt  inclined  at  19°  with  no 
greater  wear  at  the  loading  point,  the  speed  should  be  no  greater  than 
400 X. 67  =268  feet. 

TABLE  30.— REDUCED  BELT  SPEEDS  FOR  LOADING  ON  INCLINES 


FIG.  143. — Reduction  of  Velocity  of  In- 
clined Belts  to  Lessen  Cutting  and 
Abrasion. 


Angle  of  incline,  degrees  .  . 

5 

10 

13 

16 

19 

99 

Percentage  of  normal  speed  for  horizontal  belt 

91 

83 

78 

73 

67 

61 

A  slower  speed  for  steep  belts  also  reduces  the  wear  from  slip  on  the 
incline  (see  p.  142),  and  since  it  lessens  the  jostling  of  the  load  over  the 
idlers,  it  reduces  the  tendency  of  the  material  to  roll  or  slip  down  the  incline. 
(For  a  disastrous  combination  of  20°  angle  and  350-foot  speed,  see  p.  117.) 

Carrying  capacities  for  inclined  belts  should  be  calculated  with  some 
reference  to  the  lower  speeds  which  are  often  advisable,  especially  in  carry- 
ing stone,  ore  and  other  difficult  materials. 

Horizontal  Loading  Ends  for  Inclined  Belts. — Conveyors  inclined  at  about 
20°  for  coke,  large  lump  stone  and  other  difficult  materials  have  been  built 
with  a  curve  at  the  foot  of  the  slope  (see  Fig.  Ill),  so  that  the  belt  is  loaded  on  a 
short  run  which  is  nearly  or  quite  horizontal.  This  arrangement  permits  the 
belt  to  be  run  at  normal  speed,  there  is  less  cutting  and  abrasion  of  the  belt 
surface  and  the  material  is  not  so  likely  to  slip  and  roll  while  on  the  incline. 

The  curve  should  be  so  located  with  reference  to  the  loading  chute  and  be  of 


SPEEDS  FOR  PICKING  OR  SORTING  BELTS  155 

sufficient  radius  so  that  under  no  conditions  can  the  belt  lift  off  the  idlers  and 
be  cut  by  the  skirt  boards. 

The  danger  of  lifting  the  belt  is«4voided  if  the  path  of  the  belt  is  changed  by 
the  use  of  pulleys  as  in  Fig.  15,  but  the  scheme  has  several  drawbacks;  it  takes 
up  room,  it  gives  the  belt  several  extra  bends,  one  of  them  with  the  dirty  side 
of  the  belt  against  the  pulley,  and  there  is  the  added  cost  of  three  or  four 
deflector  pulleys  with  their  shafts,  bearings  and  supports. 

Speeds  for  Grain  Belts. — The  experiments  by  Westmacott  and  Lyster 
in  1865  showed  that  oats,  bran  and  flour  could  be  carried  at  speeds  up  to 
480  feet  per  minute  without  being  blown  off  the  belt  by  the  air  resistance; 
they  found  also  that  wheat  could  be  carried  at  540  feet  per  minute  safely, 
but  that  the  chaff  in  it  would  be  blown  off.  These  trials  were  made  with 
belts  12  and  18  inches  wide,  run  flat  except  for  concentrators  at  the  loading 
points. 

In  modern  practice  wheat  and  corn  are  carried  at  speeds  up  to  800  feet 
per  minute  on  belts  36  inches  and  wider;  but  on  belts  less  than  20  inches 
wide  the  speed  should  be  less  than  500  feet  per  minute.  The  main  reason 
is  that  in  chutes  suited  to  wide  belts  the  flow  of  grain  is  rapid  and  regular 
and  the  belt  can  be  loaded  full,  but  in  narrow  chutes  the  flow  is  not  so  fast 
and  even,  and  the  narrow  belt  running  faster  than  500  feet  per  minute  will 
not  take  a  full  load  nor  will  the  loading  be  uniform  along  the  run  of  the  belt. 

The  last  column  of  Table  28  represents  good  practice  in  speeds  of  grain 
conveyors. 

Speeds  for  Picking  or  Sorting  Belts. — When  belts  are  used  for  picking 
or  sorting  ores  the  speed  must  be  low  enough  to  permit  the  men  alongside 
to  pick  out  and  turn  over  pieces  on  the  belt  without  moving  from  their 
positions  and  without  stretching  too  far.  The  speed  is  generally  less  than 
50  feet  per  minute;  for  large  lumpy  material  that  must  be  turned  over 
for  examination  the  speed  may  be  25  feet  per  minute.  (See  also  p.  193.) 


CHAPTER  VIII 
DISCHARGING  FROM   THE  BELT 

Discharge  from  Belts. — The  simplest  discharge  from  a  belt  conveyor 
is  over  the  head  pulley.  The  path  of  the  material  in  leaving  the  belt  is  a 
parabola;  its  appearance  at  various  speeds  is  shown  in  Figs.  144,  145.  146, 
147.  Rules  and  diagrams  are  given  by  manufacturers'  catalogues  for  laying 
out  the  parabola  by  coordinates.  Fig.  148  and  Table  31  are  Jeffrey's. 
The  line  X —  Y  represents  the  approach  of  the  belt  to  the  discharge  pulley. 
From  the  tangent  point  Y,  where  it  meets  the  pulley,  lay  off  distances  L 
in  inches  equal  to  belt  speed  in  feet  per  minute  divided  by  100.  Distances 
A,  B,  C,  etc.,  from  the  table  measured  vertically  from  the  first,  second,  third 
point,  etc.,  locate  the  curve. 

Position  of  Chute. — In  handling  material  easily  broken,  like  sized 
anthracite  coal,  briquettes,  screened  coke,  etc.,  it  is  desirable  to  place  the 
chute  so  that  it  receives  the  discharge  without  shock  and  without  excessive 
drop.  At  the  same  time,  the  top  edge  of  the  bottom  plate  of  the  chute 
should  be  set  so  that  no  pieces  can  jam  in  the  gap  between  it  and  the  belt, 
and  in  such  a  position  that  if  the  conveyor  should  be  stopped  while 
loaded,  the  dribble  of  material  over  the  pulley  in  starting  up  at  slow  speed 
will  not  fall  into  the  gap  and  be  wasted  or  stick  there  and  damage  the  belt. 
To  a  great  extent  these  requirements  are  contradictory;  for  an  easy  delivery 
the  chute  should  be  at  1  (Fig.  148),  but  for  safety  to  the  belt  it  should  not 
be  placed  higher  than  2;  if  the  material  tends  to  stick  to  the  belt  and  is  not 
hurt  by  the  drop,  it  is  better  to  put  the  chute  at  3.  If  there  is  a  cleaning 
brush  at  the  discharge  pulley  the  chute  must  be  further  back,  as  in  Figs.  174 
and  175  so  that  at  no  time  can  material  discharged  over  the  head  pulley 
fall  directly  on  the  brush. 

Tripper  Chutes. — In  trippers  where  it  is  important  to  save  height,  the 
chute  is  usually  placed  at  position  2,  and  the  brush  is  placed  below  it  so  as  to 
throw  the  fine  stuff  clinging  to  the  belt  back  on  the  empty  run  as  it  leaves 
the  tripper. 

Choked  Chutes. — When  there  is  danger  of  material  backing  up  in  a 
choked  discharge  chute  and  then  scraping  the  belt  it  is  well  to  set  the 
upper  end  of  the  chute  some  distance  below  the  pulley,  so  that  when  the 
material  does  back  up,  it  will  overflow  from  the  top  of  the  chute  before  it 
reaches  the  belt  on  the  pulley. 

Dribble  over  End  Pulley. — When  a  belt  conveyor  delivers  to  a  bin 
through  a  tripper  it  is  never  safe  to  assume  that  all  of  the  material  will  be 
discharged  at  the  tripper  and  none  over  the  end  pulley  of  the  conveyor. 

156 


DISCHARGE  OVER  END  PULLEY 


157 


144 


145 


146 


147 

FIGS.  144-147. — Discharge  at 
24-inch  Head  Pulley  of  Belt 
Conveyor  at  Various  Speeds. 

144. — 140  feet  per  minute. 
145. — 275  feet  per  minute. 
146. — 360  feet  per  minute. 
147. — 780  feet  per  minute. 


158 


DISCHARGING  FROM  THE  BELT 


The  fine  stuff  which  clings  to  the  belt  or  which  is  brushed  off  in  the  tripper 
falls  over  the  end  pulley,  and  if  the  latter  is  not  placed  over  the  bin,  the 
dribble  outside  of  the  bin  may  be  a  nuisance.  If  it  is  necessary  to  place  the 
end  pulley  beyond  the  bin,  an  auxiliary  chute  may  be  provided  to  catch 
the  dribble. 


FIG.  148. — Path  of  Discharge  over  a  Belt  Pulley. 
TABLE    31.— VERTICAL    ORDINATES,    INCHES,   FOR  USE  WITH    FIG.    148 


A 

.43 

D 

7.72 

G 

23.64 

J 

48.24 

B 

1.93 

E 

12.06 

H 

SO.  87 

K 

58.37 

C 

4.34 

F 

17.37 

I 

39.07 

L 

69.47 

Plows  or  Scrapers. — When  belts  handle  material  like  wood  chips,  fine 
coal,  dry  chemicals,  etc.,  which  are  not  abrasive  and  which  can  be  carried 

with  little  or  no  troughing,  it  is  pos- 
sible to  discharge  them  at  various 
places  along  the  run  by  plows  or 
scrapers  set  diagonally  across  the  belt 
(Fig.  149).  The  lower  edge  of  the 
scraper  should  be  a  few  inches  above 
the  belt  and  the  actual  scraping  of 
material  done  by  a  strip  of  belting 
fastened  to  the  board  and  touching 
the  conveyor  belt.  Scrapers  are 
sometimes  hinged  at  one  end  and  bear 
against  a  stop  at  the  other,  in  which 
case  they  may  be  worked  by  a  pair  of 
pull  ropes  from  a  distant  point;  or 
they  may  be  fitted  between  a  pair  of 
vertical  guides  as  in  the  figure  and 


FIG.  149.— Discharge  from  Flat  Belt  by 
a  Diagonal  Scraper. 


transferred  from  place  to  place  to 
change  the  discharge.  With  any  construction,  a  chute  or  guard  should  be 
provided  at  each  discharge  point  to  prevent  scattered  material  from  collect- 


OBJECTIONS  TO  SCRAPERS  159 

ing  under  the  upper  run  and  fouling  the  idlers  or  else  falling  on  the  return 
belt. 

This  form  of  discharge  works >4>est  with  flat  belts  and  light  loads;  it 
has  been  used  with  Uniroll  idlers,  but  will  not  work  with  belts  troughed 
more  than  5°  or  10°.  It  has  been  used  in  places  where  the  first  discharge 
from  a  belt  came  too  close  to  the  loading  point  to  allow  a  tripper  to  be  used, 
and  on  long  conveyors  outdoors  where  it  was  not  convenient  to  install  a 
traveling  tripper. 

Objections  to  Scrapers. — The  general  objection  is,  of  course,  the  wear 
on  the  surface  of  the  belt.  A  specific  fault  of  the  construction  shown  in 
Fig.  149  is  that  if  the  material  is  heavy,  or  the  belt  troughed,  there  is  a 
component  of  pressure  at  the  scraper  which  tends  to  force  the  belt  out  of 
line  and  off  the  idlers  at  the  point  of  discharge.  This  can  be  avoided  by 
making  the  scraper  or  plow  symmetrical  with  a  V  point  to  discharge  on  both 
sides  of  the  belt.  With  this  construction,  the  discharge  is  not  spread  over 
so  much  length,  but  a  disadvantage  is  that  the  ends  of  the  rubber  scraping 
strips  which  bear  on  the  belt  may  catch  at  the  belt  splice  or  at  worn  places 
in  the  belt  and  do  damage  to  the  belt  or  else  be  worn  off  or  torn  loose. 

Traveling  Plows. — In  some  European  boiler  houses  the  bunker  is  served 
by  a  flat  belt  which  runs  through  a  movable  carriage  equipped  with  a 
V-point  plow  and  a  two-way  chute.  The  movement  of  the  carriage  is 
controlled  from  the  floor  of  the  boiler  room  by  a  hand-power  winch  operating 
a  pair  of  pull  ropes.  An  indicator  on  the  winch  shows  the  position  of  the 
carriage,  and  it  is  not  necessary  for  a  man  to  go  aloft  to  change  the  position 
of  discharge.  Besides  that,  the  carriage  is  cheaper  than  a  tripper  and 
takes  up  less  head  room. 

Comparison  with  Trippers. — As  compared  with  a  tripper,  a  plow  causes 
more  wear  on  the  surface  of  the  belt,  but  it  does  not  tend  to  separate  the 
plies  of  the  belt  by  breaking  down  the  friction  layers  between  them  by  reverse 
bending,  as  a  tripper  with  its  small  pulleys  often  does.  If  the  material  is 
fine  and  not  abrasive,  the  life  of  the  belt  would  ordinarily  be  determined 
by  the  life  of  its  friction  and  not  by  wear  on  the  surface.  In  such  a  case 
it  may  be  ultimately  more  economical  to  use  a  scraper  and  put  some  wear 
on  the  belt  surface  so  as  to  equalize  in  some  degree  the  external  and  internal 
wear  of  the  structure  of  the  belt.  Even  though  the  life  of  the  belt  is  short- 
ened, it  may  still  be  economy  to  pay  for  belting  rather  than  for  a  tripper 
and  the  necessary  attendance,  maintenance  and  repairs. 

Distribution  to  Separate  Bins. — When  a  belt  is  used  to  distribute 
material  to  a  series  of  small  bins  a  traveling  tripper  is  at  a  disadvantage 
because  too  much  time  is  lost  in  transferring  the  tripper  from  place  to  place 
and  in  making  sure  that  the  belt  is  empty  when  the  tripper  moves  across 
the  clear  space  between  the  bins,  so  that  the  tripper  will  not  discharge 
material  between  the  bins.  There  is  also  the  expense  of  an  attendant  to 
set  the  tripper  and  make  sure  that  it  is  clamped  to  the  rails  so  tight  that  it 
will  not  work  loose  and  travel  with  the  belt.  Fixed  trippers  set  over  each 
bin  are  sometimes  used,  but  if  the  service  is  hard  and  continuous  they  hurt 


160  DISCHARGING  FROM  THE  BELT 

the  belt  by  the  repeated  reverse  bending  and  by  the  repeated  delivery  of 
material  back  on  the  belt  when  the  discharge  point  is  beyond  one  or  more 
of  the  trippers.  The  by-pass  chutes  furnished  with  trippers,  traveling  or 
fixed,  do  not  deliver  material  back  to  the  belt  at  belt  speed  and  the  wear 
on  the  belt  is  greater  than  from  a  well-designed  loading  chute  (see  Fig.  159). 
When  fine  material  is  to  be  distributed  to  a  series  of  small  bins,  as 
in  delivering  foundry  sand  to  the  hoppers  of  molding  machines,  a  number  of 
scrapers  operated  by  pull-ropes  will  sometimes  do  the  work  at  less  cost 
and  with  greater  convenience  than  any  arrangement  of  trippers,  traveling 
or  fixed. 

Other  Discharge  Devices. — An  old  device,  patented  by  Palmer  in  1888, 
is  shown  in  Fig.  150.  When  the  idler  pulley  is  tilted,  the  material  slides 

off  the  belt,  but  the  discharge  can- 
not be  located  with  accuracy  because 
it  begins  and  ends  as  a  dribble  over 
the  edge  of  the  belt  and  the  bulk  of 
it  is  spread  over  some  distance  of 
travel.  The  scheme  is  used  in  a 
few  places  with  belts  less  than  24 
inches  wide  to  discharge  fine  dry 
material  into  large  bins  where  the 
position  of  discharge  is  not  im- 

Idler  to  Discharge^        P°rtaf  *'     The  retu/ n  **?*  ™st   |» 
Material  from  a  Belt.     (Jeffrey.)  guarded  against  the   spill  from  the 

upper  run. 

A  device  similar  to  a  plow  is  shown  in  the  Brotz  patent  of  1912.  It 
consists  of  a  horizontal  disk  of  steel  plate  mounted  on  a  vertical  shaft  and 
extending  over  the  belt  in  such  a  way  that  as  the  disk  revolves  it  will  take 
material  from  the  belt  and  deliver  it  to  one  side.  It  was  tried  once  in  a 
foundry  to  remove  sand  from  a  flat  belt  to  a  series  of  small  bins.  The  disks 
were  driven  by  frictional  contact  with  the  belt  and  could  be  moved  into  or 
out  of  operating  position.  They  were  not  satisfactory,  and  were  finally 
replaced  by  scrapers  set  diagonally  across  the  belt  and  controlled  by  pull- 
cords  from  the  floor  below. 

Discharge  by  Inverting  the  Belt. — Discharge  at  points  along  the  run 
of  a  belt  conveyor  can  be  effected  by  the  use  of  fixed  trippers.  If 
they  are  set  in  series  to  discharge  at  several  points  it  is  necessary  to 
provide  all  but  the  last  with  a  by-pass  chute  to  reload  material  on  the 
belt  and  fit  them  with  flap  gates  to  divert  the  stream,  or  else,  as  in  Fig.  151, 
let  the  main  chute  fill  up  and  overflow  into  the  by-pass  chute.  This  was 
the  arrangement  adopted  in  an  American  cement  plant  built  about  1902 
where  a  stock-house  was  filled  by  a  belt  running  through  a  long  series  of 
fixed  trippers.  The  travel  of  the  cement  in  the  by-pass  chute  was  so  short 
that  it  did  not  acquire  any  speed,  and  hence  it  wore  the  belt.  In  applying, 
in  1907,  for  a  patent  on  a  rotating-drum  device  to  replace  the  by-pass 
chutes  on  these  trippers  and  to  throw  the  cement  back  on  the  belt  with 


USE  OF  FIXED  TRIPPERS 


161 


When  Main  Chute 
fills  up  material 


FIG.  151.— Fixed  Tripper 
with  By-pass  Chute. 


some  velocity  in  the  direction  of  travel,  the  engineer  of  the  plant  says, 
"  I  find  that  the  belts  become  very  rapidly  worn,  since  at  each  discharge 
station  the  material  falling  fromf^the  upper  to  the  lower  run  of  the  belt 
requires  to  be  moved  from  a  state  of  rest  to 
the    speed    of  the  belt."     This  has  been  the 
experience   of   others  using   fixed  trippers  with 
by-pass  chutes,  and  at  present  they  are  seldom 
used.     A   traveling   tripper  bends  the  belt  less 
than  a  series  of  fixed  trippers,  avoids  all  or  most 
of  the  reloading  on  the  belt  and  is  likely  to  cost 
less  than  three  or  four  fixed  trippers  with  their 
chutes.     At  any  tripper,  the  material  must  be 
lifted  from  2  to  5  feet  in  order  to  effect  a  dis- 
charge.    A   traveling   tripper   does    this    once, 
but  a  series  of  fixed  trippers  does  it  oftener. 

Hence  more  power  is  required  to  drive  the  conveyor  through  such  a  series 
of  fixed  trippers. 

Use  of  Fixed  Trippers. — When,  however,  a  belt  discharges  to  a  series  of 
small  bins,  or  through  hatches  in  a  floor  to  tanks  or  chutes  beneath  the 
floor,  it  may  not  be  convenient  to  use  a  traveling  tripper,  because  in  order 
to  avoid  spill  on  the  floor  the  belt  must  be  empty  when  the  tripper  is  moved. 
In  handling  grain  in  American  "  elevators  "  it  is  customary  to  stop  the  flow 
of  grain  to  the  belt  when  the  tripper  is  moved  between  spouts,  but  in  some 
manufacturing  plants  it  is  impossible  to  shut  off  the  feed  to  the  belt  without 
costly  interruption  of  the  processes.  In  such  cases  it  is  good  practice  to 
use  a  fixed  tripper  over  each  discharge  hatch  and  suffer  the  added  wear  on 
the  belt. 

Stationary  Trippers  with  Movable  Pulleys. — Some  of  the  objections  to  a 
stationary  tripper  with  fixed  pulleys  can  be  avoided  by  making  the  upper 


FIG.  152.— Stationary  Tripper  with  One 
Pulley  Movable  to  Effect  Discharge 
or  Allow  Material  to  Pass  By. 


FIG.  153. — Cookman-Neall  Tripper  for 
Grain  Belt. 


pulley  movable,  either  as  in  Fig.  152,  where  the  pulley  swings  from  its  idle 
position  at  A  to  its  operating  position  at  B  around  an  axis  on  which  is 


162  DISCHARGING  FROM  THE  BELT 

mounted  the  other  pulley  C,  or  as  in  the  Cookraan-Neall  tripper  of  1901. 
In  this  device,  which  was  used  at  the  Washington  Avenue  grain  elevator  in 
Philadelphia  for  a  number  of  years,  the  power  to  lift  the  discharge  pulley 
is  taken  from  the  return  belt.  Turning  the  hand  wheel  (Fig.  153)  depresses 
73  and  forces  the  return  belt  into  driving  contact  with  A2.  A  chain  running 
from  H  to  G  drives  a  pair  of  vertical  screws  through  reversing  clutches  to 
raise  or  lower  E. 

Traveling  Trippers. — The  earliest  trippers  used  in  this  country  were  sta- 
tionary (see  page  7).  Movable  trippers  came  into  use  after  1870.  The 
first  of  these  were  similar  to  Westmacott's  tripper  (see  p.  8).  Fig.  154 
shows  one  used  at  Duluth  in  the  early  eighties  (T.  W.  Hugo,  Transactions 
A.  S.  M.  E.,  1884).  It  consisted  of  a  pair  of  cast-iron  side  frames  that 
carried  two  pulleys  which  by  means  of  the  hand  wheel  and  worm  gear 


FIG.  154. — Hand-propelled  Tripper  with  Pulleys  Adjustable  for  Reversible  Discharge. 

could  be  rotated  from  the  idle  position  A  A  to  either  of  the  working  positions 
BB  or  CC.  With  the  pulleys  at  A  A,  the  loaded  belt  would  pass  through 
the  tripper  without  being  acted  upon;  with  the  pulleys  at  BB,  grain  coming 
from  the  right  would  be  discharged  into  the  chute;  when  the  belt  was 
reversed  to  carry  grain  from  the  left,  the  chute  was  transferred  to  the  other 
side  of  the  frame  and  the  pulleys  were  swung  to  the  position  CC.  The 
frame  was  pushed  by  hand  to  the  discharge  point,  while  the  belt  was  slack, 
and  was  fastened  to  the  floor  by  hooks  and  turnbuckles;  the  pulleys  were 
raised  to  the  working  position  and  then  the  conveyor  take-ups  were 
tightened. 

Self-propelled  Trippers. — William  B.  Reaney  (see  p.  8)  designed  the 
first  self-propelled  tripper  in  1876.  It  was  like  Fig.  154  in  having  the 
pulleys  adjustable  for  discharging  a  reversible  belt,  but  it  was  new  in 
taking  power  from  the  conveyor  belt  to  propel  the  frame  backward  and 
forward.1 

1  Communicated  to  the  author  by  Mr.  George  M.  Moulton  of  Chicago,  who  with  his 
father,  John  T.  Moulton,  built  an  elevator  at  Duluth  in  1869,  the  Canton  elevator  in  1876 
and  many  other  important  grain  elevators. 


SELF-PROPELLED  TRIPPERS 


163 


After  a  few  years  of  successful  use  at  the  Canton  Elevator,  self-propelled 
traveling  trippers  came  into  general  use,  and  for  simplicity  in  construction 
they  were  generally  made  with  pulleys  on  shafts  fixed  in  position.  In  the 
older  hand-propelled  trippers  it  was  necessary  to  swing  the  pulleys  out  of 
position  in  order  to  push  the  frame  easily,  but  that  was  not  necessary  with 
power-driven  trippers.  At  first,  separate  friction  clutches  or  jaw  clutches 


Hand  Lever  for  Track  Clamps  _ 


Hand  Lever  for  Friction  Wheels 
on  Rocker  Anus 


I      Reversible  Chain  Drive  to  Geared  Track  Wheels 

FIG.  155. — 2-pulley  Tripper  for  High-speed  Grain  Conveyor. 


were  used  on  each  pulley  shaft  to  drive  chains  leading  to  the  track  wheels, 
but  later  the  modern  style  with  paper  and  iron  friction  wheels  came  into 
use.  Fig.  155  shows  a  modern  friction-driven  tripper  for  high-speed  grain 
belts  with  geared  track-wheels.  When  a  tripper  is  required  to  discharge 
from  a  reversible  belt  it  is  simpler  and  more  convenient  to  use  four 
pulleys  rather  than  the  two  movable  pulleys  of  the  older  style.  Fig.  156 


Hand  Levers  for 
JVack  Clamps  and 
£ccentric  Shaft. 


14*PuIUva 


Shaft  wltft 
on  Wheel 


I. 

FIG.  156. — 4-pulley  Tripper  for  Reversible  High-speed  Grain  Conveyor. 

shows  a  modern  four-pulley  tripper  controlled  by  two  hand  levers,  one  for 
the  friction  wheels,  one  for  the  rail  clamp.  The  hood  over  the  chute  is 
pivoted  and  can  be  tilted  to  receive  the  grain  from  either  side.  This  style 
of  tripper  is  seldom  used  for  material  other  than  grain;  the  pulleys  are 
only  12  or  14  inches  in  diameter,  too  small  for  belts  thicker  than  the  4-ply 
generally  used  on  grain  conveyors.  A  tripper  typical  of  those  used  for 
materials  like  coal,  crushed  stone,  etc.,  is  shown  in  Fig.  157.  The  frame  is 


164 


DISCHARGING  FROM  THE  BELT 


low,  the  machinery  simple,  and  since  the  opposite  track  wheels  are  mounted 
on  separate  pins  instead  of  an  axle  the  tripper  tracks  can  be  set  low  without 
interference  between  the  tripper  and  the  troughing  idlers.  The  friction 
wheels  of  compressed  fiber  board  at  A  and  B  are  7  inches  in  diameter; 
the  operating  shaft  C  is  mounted  in  eccentric  sleeve  bearings  which  by  means 
of  the  hand  lever  D  can  be  moved  in  one  direction  or  the  other  to  force  the 
iron  friction  wheel  E  into  contact  with  A  or  B  to  propel  the  frame  either 
backward  or  forward.  There  is  a  chain  drive  on  each  side  of  the  frame 
connecting  the  operating  shaft  with  one  or  both  track  wheels;  the  friction 
wheel  E  is  18  inches  in  diameter,  and  the  chain  drive  is  such  that  in  a  tripper 


FIG.  157. — Self-propelled  Tripper  with  Friction  Drive.     (Link-Belt  Company.) 

equipped  with  16-inch  belt  pulleys,  the  forward  travel  is  about  22  feet  per 
minute  and  the  backward  travel  26  feet. 

Worm-geared  Trippers. — The  original  worm-geared  tripper  patented 
by  Ticknor  and  Baldwin  in  1904  has  on  one  end  of  the  lower  pulley  shaft  a 
bevel  gear  which  meshes  with  two  bevel  pinions  on  a  shaft  lying  parallel 
to  the  belt  and  driving  each  truck  axle  through  a  set  of  worm  gears.  The 
bevel  pinions  on  the  worm  shaft  may  be  clutched  to  it  by  the  motion  of  a 
sliding  jaw  so  as  to  turn  the  worm  shaft  in  either  direction,  or  else  they  are 
shifted  bodily  along  a  key  to  engage,  one  or  the  other,  with  the  driving 
gear.  The  driving  mechanism  is  all  enclosed  and  the  appearance  is  good. 
The  positive  drive  through  gears  is  objectionable  for  high-speed  belts,  but 
when  the  belt  speeds  are  under  350  feet  per  minute,  and  the  tripper  pulleys 


AUTOMATIC  SELF-REVERSING  TRIPPERS  165 

are  of  good  size,  the  arrangement  works  well  without  racking  the  tripper 
too  much. 

Automatic  Self-reversing  Trippers. — In  the  worm-geared  tripper  the 
travel  of  the  clutch  parts  is  very  short  and  the  motion  is  given  by  a  short 
lever  projecting  vertically  from  the  gear  box.  It  is  therefore  easy  to  give 
the  tripper  an  alternating  backward  and  forward  motion  during  the  travel 
of  the  belt  by  arranging  stops  along  the  run  of  the  conveyor  to  engage  the 
shift  lever.  This  makes  an  automatic  self-reversing  tripper  that  will 
distribute  the  discharge  from  a  belt  over  the  length  of  a  bin  or  a  stock  pile 
without  the  attention  of  an  operator  to  set  and  reset  the  tripper. 

Similar  automatic  self-reversing  trippers  are  made  by  the  Stephens- 
Adamson  Manufacturing  Co.  with  paper  and  iron  friction  wheels,  by  the 
Link-Belt  Company  with  shifting  clutches,  by  Jeffrey  Manufacturing  Co. 
with  bevel  gears  and  a  reversing  shaft,  etc. 

In  filling  very  long  bins,  an  automatic  self-reversing  tripper  is  a  con- 
venience; but  in  boiler  houses  of  ordinary  size  it  is  often  better  to  avoid  the 
complication  of  parts  and  use  a  simple  tripper  which  can  be  clamped  to 
the  track  while  it  fills  a  part  of  the  bin.  In  many  cases  an  automatic  self- 
reversing  tripper  does  not  reduce  the  cost  of  attendance;  it  does  add  to  the 
first  cost  of  the  plant  and  increases  the  cost  of  up-keep. 

Tripper  Pulleys. — Old  grain  belt  trippers  had  12-inch  diameter  pulleys 
as  "  standard."  The  custom  persists,  and  some  are  still  built  so.  They 
work  fairly  well  with  the  4-ply  belts  generally  used  for  grain  conveyors, 
but  there  is  no  doubt  that  the  belts  would  last  longer  if  the  pulleys  were 
4  or  5  inches  in  diameter  for  each  ply  of  the  belt  (see  p.  127),  that  is,  16  or 
20  inches  in  diameter  for  4-ply  belts.  Grain-conveyor  belts  do  not  often 
fail  by  cutting  or  abrasion,  but  rather  from  splices  pulling  apart  and  from 
separation  of  the  plies  due  to  failure  of  the  friction  rubber.  Both  of  these 
troubles  are  aggravated  and  the  life  of  belts  shortened  by  the  use  of  small 
pulleys  in  trippers.  Large  pulleys  cost  a  little  more,  but  they  save  more 
than  their  added  cost  in  the  increased  life  of  belts  and  the  avoidance  of  belt 
troubles  and  repairs. 

For  materials  other  than  grain,  the  case  is  different;  the  belts  are  gener- 
ally thicker  than  4-ply,  and  the  splices  hold  better;  moreover,  the  life  of 
the  belt  is  often  determined  by  the  surface  wear  rather  than  the  separation 
of  the  plies.  In  such  cases  it  would  not  always  be  economy  to  make  pulleys 
4  or  5  inches  in  diameter  per  ply  of  belt,  especially  since  belts  for  heavy  work 
are  frequently  6-,  7-  or  8-ply  thick.  The  tripper  would  become  too  large  and 
too  heavy,  and  the  life  of  the  belt  would  not  be  economically  prolonged. 
But  while  there  may  be  doubt  about  making  tripper  pulleys  30  inches  in 
diameter  for  6-ply  belts,  for  instance,  it  is  certain  that  the  ratio  of  diameter 
to  ply  should  never  be  less  than  3  to  1,  that  is,  18-inch  diameter  for  a  6-ply 
belt.  There  are  many  cases  where  a  ratio  of  4  to  1  would  be  better,  even 
in  the  class  of  work  considered  here.  Some  judgment  is  needed  in  selecting 
the  sizes  of  tripper  pulleys;  manufacturers'  "  stock  sizes  "  are  frequently 
too  small  for  good  work. 


166 


DISCHARGING  FROM  THE  BELT 


Tripper  chutes  are  made  in  various  ways;  for  discharge  to  one  side,  to 
both  sides  by  a  split  discharge,  or  alternately,  or  in  such  a  way  as  to  put  the 
material  back  on  the  belt.  Ordinary  two-way  chutes  on  trippers  for  coal, 
stone,  ores,  etc.,  are  generally  fitted  with  a  flap  gate  (Fig.  158)  for  discharge 
to  either  side  alternately.  When  the  material  is  put  back  on  the  belt  for 
discharge  over  the  end  pulley  of  the  conveyor,  two  flap  gates  are  used 
(Fig.  159).  The  delivery  of  material  to  the  belt  in  this  way  is  not  accord- 
ing to  the  best  methods  of  loading  a  belt,  because  the  chute  is  necessarily 
short  and  the  material  does  not  acquire  much  velocity  in  the  direction  of 
belt  travel. 

Tripper  chutes  are  often  set  with  the  upper  edge  at  position  2  (Fig.  148) 
so  as  to  save  height  in  the  frame  and  lift  of  material  in  passing  through  the 
tripper;  there  are,  however,  several  disadvantages.  If  the  belt  is  stopped 
while  loaded,  starting  again  at  slow  speed  causes  material  to  fall  into  the 


FIG.  158. — Tripper  Chute  to  Discharge 
to  Either  Side. 


FIG.   159. — Tripper  Chutes  to  Discharge 
to  Either  Side  or  Back  on  the  Belt. 


space  between  the  belt  and  the  chute,  and  if  the  pieces  wedge  there 
and  are  sharp  and  angular  the  belt  may  be  cut  or  torn.  When  a  chute 
is  placed  at  position  2,  the  clearance  is  generally  made  small  to  catch 
all  of  the  material  from  the  belt.  It  has  happened  that  a  blistered  belt 
has  caught  at  the  edge  of  the  chute,  pulled  the  tripper  loose  from  the 
track  where  it  was  clamped,  and  caused  a  serious  accident.  It  is  better  to 
put  the  upper  edge  of  the  chute  at  a  position  lower  than  2  so  as  to  catch 
all  of  the  spill  and  yet  with  clearance  enough  to  avoid  catching  torn  or 
blistered  places  on  the  belt,  or  a  loose  belt-fastener. 

Tripper  Brushes. — Trippers  that  handle  sharp  gritty  material,  especially 
if  wet,  should  be  fitted  with  rotary  cleaning  brushes,  or  else  the  lower 
pulley  will  force  sharp  particles  into  the  cover  of  the  belt.  Since  the 
brush  must  revolve  against  the  travel  of  the  belt,  it  is  usually  driven  from 
the  upper  pulley  shaft  by  a  chain  which  can  be  shortened  when  the  brush 
is  raised,  to  compensate  for  wear. 

Belts  handling  sharp  wet  sand  have  been  ruined  for  lack  of  a  brush 
in  the  tripper  (see  p.  199).  It  must  be  said,  however,  that  a  brush  in  a 
tripper  needs  constant  care  and  attention  to  keep  it  in  working  order. 


BELTS  RUNNJNG  CROOKED  THROUGH  TRIPPER  167 

Belts  Running  Crooked  through  Tripper. — When  a  belt,  instead  of  run- 
ning straight  through  a  tripperf  runs  off  to  one  side  so  much  as  to  scrape 
its  edges,  it  is  well  to  look  to  the  .gauge  of  the  tripper  rails.  If  there  is  too 
much  clearance  between'the  rails  and  the  wheel  flanges,  the  tripper  frame 
may  pull  out  of  square  with  the  belt.  The  belt  will  also  run  crooked  if  the 
ends  of  the  belt  are  not  cut  square  at  the  splice  or  if  the  tripper  frame  is  not 
stiff  enough  to  resist  distortion. 

Trippers  should  be  made  so  wide  that  if  the  belt  does  run  off  the  pulleys 
for  an  inch  or  two  it  will  not  scrape  its  edges  on  the  side  of  the  discharge 
chute  or  on  the  propelling  mechanism  of  the  tripper.  Edge  rolls  are  some- 
times used  to  guide  the  belt  in  a  tripper,  but  they  should  be  avoided  if 
possible,  as  they  cause  wear  on  the  edges  of  the  belt. 

Trailers. — Large  trippers  for  heavily  loaded  belts  are  sometimes  made 
with  trailers  which  are  rear  extensions  of  the  tripper  frame  carrying  several 


FIG.  160. — Large  Belt  Tripper  with  Trailer  Extension. 

sets  of  idlers  intended  to  support,  the  belt  as  it  rises  into  the  tripper  (Fig.  160). 
In  many  cases  the  trailer  is  of  little  or  no  use,  because  when  the  load  on  the 
conveyor  changes,  the  belt  lifts  off  the  trailer  as  shown  in  the  figure.  The 
same  thing  may  happen  when  the  tripper  approaches  the  head  of  the 
conveyor.  The  belt  tension  is  greater  there,  and  as  a  consequence  the  belt 
sags  less  on  the  lift  into  the  tripper  and  does  not  touch  the  idlers  on  the 
trailer. 

Unusual  Forms  of  Traveling  Trippers. — In  1901  a  patent  was  issued  to 
Humphreys  on  a  tripper  "  provided  with  idler  pulleys  over  which  the  belt 
runs,  and  means  actuated  by  the  one  or  more  of  said  pulleys  for  giving 
travel  to  the  tripper."  This  patent  was  granted  without  full  knowledge 
of  the  prior  use  of  traveling  trippers  by  Reaney  and  others;  it  led  to  mis- 
understandings and  stimulated  the  invention  of  several  traveling  trippers 
propelled  by  haulage  ropes  instead  of  taking  power  from  the  belt  Some 
were  made  and  used,  but  the  driving  machinery  was  more  complicated  than 
that  of  a  self-propelled  tripper;  with  a  wider  knowledge  of  what  bad  already 


168 


DISCHARGING  FROM  THE  BELT 


been  done  in  grain-belt  trippers,  the  apparent  need  for  these  special  trippers 
passed  away. 

Proal,  in  1907,  patented  a  worm-geared  tripper  for  a  reversing  belt 
with  an  upper  fixed  pulley  from  which  the  frame  was  driven,  and  two  other 
pulleys  on  a  swinging  frame  to  deflect  the  belt  in  one  direction  or  the  other. 
Morton,  in  1907,  patented  a  similar  device  with  two  pulleys  rocking  around 
an  intermediate  center.  In  1907  Robins  and  Baldwin  patented  a  tripper 
designed  to  travel  back  and  forth  over  a  series  of  separated  bins  and  dis- 
charge to  the  bins  only  and  not  in  the  spaces  between  the  bins.  The 
chutes  of  the  tripper  were  to  be  made  large  to  act  as  storage  reservoirs; 
gates  at  the  lower  ends  of  the  chutes  were  closed  while  the  tripper  traveled 
between  the  bins,  but  open  while  over  the  bins.  Neither  of  these  three 
devices  has  come  into  practical  use. 

The  Messiter  patent  841558,  of  1907,  discloses  an  automatic  self- 
reversing  tripper  designed  to  travel  in  one  direction  at  the  speed  of  the  belt, 


ro  o  ol 


JL 


U  LJ  U 

FIG.  161. — Tripper  for  High-speed  Travel  and  Quick  Reverse. 

and  at  a  definite  speed  in  the  opposite  direction,  with  a  prompt  reversal 
at  each  end  of  the  travel.  In  Fig.  161  the  tripper  frame  carries  four  idle 
wheels  which  travel  on  a  track  somewhat  higher  than  the  belt  idlers.  The 
upper  tripper  pulley  is  fixed  in  position;  the  lower  pulley  is  mounted  on  a 
shaft  capable  of  a  short  distance  of  vertical  movement.  This  movement  is 
controlled  by  an  arm  26  and  a  set  of  toggle  levers.  When  the  arm  is  up,  the 
toggle  is  closed  and  the  shaft  is  forced  down,  so  that  a  flanged  wheel  at 
each  end  of  the  shaft  engages  the  track  rail,  and  since  the  tripper  pulley 
which  is  fastened  to  the  shaft  travels  counter-clockwise,  the  frame  travels 
against  the  motion  of  the  belt  and  discharges  material.  At  the  end  of  the 
travel  a  cam  track  32  depresses  the  arm  26,  opens  the  toggle  joint  and  allows 
a  pair  of  springs  to  lift  the  track  wheels  from  the  track  against  a  pair  of 
brake  blocks.  These  brakes  stop  the  rotation  of  the  lower  tripper  pulley 
without  shock,  and  the  tripper  reverses  and  travels  forward  with  the  belt 
at  belt  speed.  On  the  forward  travel,  no  material  is  discharged  from  the 
belt,  but  at  the  end  of  this  travel  the  arm  26  is  raised  by  the  cam  track  31, 
the  brakes  are  released,  the  track  wheels  are  depressed,  the  tripper  is  reversed 
without  shock  and  the  discharge  of  material  begins  again. 


LENGTH  REQUIRED  FOR  A  TRIPPER 


169 


This  tripper  is  used  in  the  Messiter  patent  bedding  system  at  a  number 
of  copper  smelters  to  form  longitudinal  piles  of  ore,  fuel  and  flux  in  layers. 
With  a  definite  and  uniform  loajj  on  the  belt,  a  positive  rate  of  tripper 
travel  and  a  prompt  reversal  at  each  end  of  the  travel,  the  various  materials 
are  deposited  uniformly  so  that  each  foot  of  length  of  the  pile  is  the  same 
in  composition,  and  when  properly  reclaimed  can  be  treated  alike  in  the 
smelting  operations.  This  tripper  is  more  positive  in  its  travel  than  one 
driven  by  friction  wheels,  and  will  reverse  at  high  speed  without  shock, 
a  feature  impossible  with  trippers  driven  by  clutches  and  gears. 

Length  Required  for  a  Tripper. — Diagrams  of  traveling  belt  trippers 
given  in  manufacturers'  catalogues  show  the  distance  from  the  chute  at  the 
front  end  to  the  point  at  which  the  straight  slope  of  the  belt  rising  into  the 
tripper  meets  the  line  of  the  horizontal  belt.  This  distance  (dimension  A, 
Fig.  162)  is  from  14  to  18  feet;  but  in  a  horizontal  conveyor,  the  distance  B 
from  the  center  of  the  chute  to  the  point  at  which  the  belt  begins  to  lift 


Horizontal  Belt 

Starts  to   Rise 

Her 


FIG.  162. — Location  of  First  Point  of  Discharge  through  a  Tripper  with  Reference  to 
the  Loading  Point  of  a  Belt. 


off  the  idlers  and  curve  up  into  the  tripper  may  be  5  to  12  feet  more  than 
the  distances  given  in  the  tables  and  diagrams.  This  is  shown  in  Fig.  160 
where  the  length  is  over  25  feet. 

Location  of  First  Discharge  Point. — The  point  at  which  the  belt  begins 
to  lift  off  the  idlers  in  a  horizontal  conveyor  helps  to  fix  the  place  of  the 
first  discharge  through  a  tripper,  because  the  tripper  can  not  come  any 
nearer  to  the  loading  point  without  danger  of  lifting  the  belt  under  the 
loading  chute  or  the  skirt-boards.  If  the  belt  should  be  lifted  by  the 
tripper's  coming  too  close,  it  will  be  scraped  or  cut  and  perhaps  ruined  in  a 
few  minutes. 

It  is  possible  to  prevent  the  tripper  from  coming  too  close  to  the  loading 
chute  by  using  stops  clamped  to  the  tripper  rails,  but  there  is  always  some 
uncertainty  about  the  point  at  which  the  belt  will  begin  to  lift,  because 
if  it  is  lightly  loaded,  or  if  it  is  pulled  tight  by  careless  use  of  the  conveyor 
take-ups,  or  in  an  effort  to  get  more  driving  effort  at  the  drive  pulley,  the 
belt  will  lift  sooner  and  span  over  a  greater  distance. 


170 


DISCHARGING  FROM  THE  BELT 


To  avoid  these  difficulties,  it  is  customary  to  depress  the  foot  ends  of 
horizontal  conveyors  when  ^the  first  discharge  comes  close  to  the  loading 
point.  In  Fig.  162  B  represents  the  distance  at  which  the  belt  begins 
to  lift  from  a  horizontal  run,  but  by  humping  the  conveyor  and  loading  on  a 
short  incline  the  distance  is  reduced  to  A,  and  the  point  of  first  discharge 
is  brought  closer  to  the  loading  point  by  approximately  B — A.  Stops 
should  still  be  used  to  limit  the  movement  of  the  tripper  (see  Fig.  163) 
because  while  the  depressed  end  of  the  conveyor  does  prevent  fluctuations 
in  belt  tension  from  affecting  the  angle  of  approach  to  the  tripper,  it  can 


FIG.  163. — Belt  Conveyor  with  Depressed  Loading  End,  and  Stops  to  Limit  Travel  of 

Tripper. 

not  be  depended  upon  to  stop  the  travel  of  the  tripper  and  prevent  it 
from  lifting  the  belt  off  the  idlers  on  the  short  incline. 

Horizontal  conveyors  with  depressed  loading  ends  are  often  used  in 
filling  short  bins  where  the  head  room  under  a  roof  is  small  or  where  it  is 
important  to  bring  the  position  of  first  discharge  as  close  as  possible  to  the 
loading  point.  There  are,  however,  some  drawbacks  to  this  plan;  it 
introduces  another  bend  in  the  belt,  and,  what  is  sometimes  more  objec- 
tionable, loading  on  an  incline.  When  the  short  end  is  inclined  at  17° 
or  18°  to  match  the  angle  of  straight  approach  to  the  tripper  the  material 
cannot  be  delivered  with  proper  velocity  in  the  direction  of  belt  travel. 
At  high  speeds  of  belt  travel  the  lumps  roll  around  longer  before  they 
acquire  belt  speed  and  the  skirt-boards  must  be  made  longer  on  that  account. 
All  this  means  added  wear  on  the  belt. 

When  the  position  of  first  discharge  is  more  than  25  or  30  feet  from  the 
end  of  the  skirt-boards  in  a  horizontal  conveyor  it  is  not  generally  necessary 
to  depress  the  loading  end,  but  for  shorter  distances  it  is  better  to  depress 


DEVICES  TO  INCREASE  THE  RANGE  OF  DISCHARGE 


171 


the  end  and  suffer  the  added  wear  on  the  belt  rather  than  run  the  risk  of 
spoiling  the  belt  by  accidentally  lifting  it  under  the  loading  chute  or  the 
skirt -boards.  „& 

Fig.  164  shows  the  loading  end  of  a  30-inch  belt  conveyor  in  a  power 
house  where  the  foot  pulley  could  not  be  depressed  below  the  level  of  the 


FIG.  164. — Depressing  the  Upper  Run  of  a  Belt  to  Permit  Loading  Close  to  Travel  of 
Tripper.     (Heyl  and  Patterson,  Inc.) 

conveyor.  This  arrangement  with  one  depressor  pulley  accomplishes  all 
that  a  depressed  end  does  and  puts  no  more  bends  in  the  belt.  The  first 
discharge  in  this  case  comes  14  feet  from  the  end  of  the  bin  and  23  feet  from 
the  foot  pulley. 

Devices  to  Increase  the  Range  of  Discharge  from  a  Tripper. — In  storing 
soft  coal,  where  it  is  desirable  to  limit  the  depth  of  pile  to  reduce  the  risk 
of  fire,  or  where  it  is  desired  to  fill  a  wide  storage  building  from  a  central 
conveyor,  or  where  there  are  objec- 
tions to  putting  the  conveyor  on  a 
high  frame  or  trestle,  it  is  possible 
to  increase  the  quantity  stored  by 
fitting  the  tripper  with  an  auxiliary 
conveyor  to  carry  the  discharge  off 
to  one  or  both  sides.  Fig.  165  shows 
the  Blaisdell  device  patented  1903; 
the  tripper  is  mounted  on  a  wide- 
gauge  track  and  fitted  with  an  in- 
clined belt  conveyor  to  pile  the 
material  off  to  one  side.  In  the 

Moss  patent  of  1907  the  scheme  is  similar,  but  the  boom  which  carries  the 
conveyor  is  mounted  on  a  turntable  in  the  tripper  frame  and  is  hinged  to 
move  up  and  down.  The  auxiliary  belt  will  therefore  pile  material  over  a 
considerable  area  at  one  setting  of  the  tripper.  In  another  arrangement 
used  by  Weller  Manufacturing  Co.,  Stephens-Adamson  Manufacturing 
Co.  and  others,  the  tripper  carries  a  reversible'  belt  conveyor  on  a  frame 
which  can  be  racked  in  and  out  at  right  angles  to  the  main  conveyor, 
and  thus  discharge  material  at  various  distances  on  each  side  of  the  center 
line. 


FIG.  165. — Traveling  Auxiliary  Belt  to  In- 
crease the  Range  of  Discharge  from  a 
Conveyor. 


172  DISCHARGING  FROM  THE  BELT 

Extensions  of  these  ideas  are  shown  in  other  arrangements  for  dis- 
tributing materials.  The  Blaisdell  patent  of  1902  discloses  a  main  conveyor 
running  along  a  row  of  leaching  or  cyaniding  tanks  and  discharging  to  a 
shorter  conveyor  which  spans  the  width  of  the  tank.  This  conveyor  may 
carry  a  tripper  for  distribution  to  the  tanks  and  its  traveling  frame  is  con- 
nected to  the  tripper  of  the  main  conveyor  so  as  to  maintain  the  two  con- 
veyors in  proper  relation  to  deliver  to  any  point  in  any  of  the  tanks.  In 
the  Dodge  device  of  1904  a  belt  conveyor  on  a  low  structure  discharges  to  a 
flight  conveyor  on  a  traveling  cantilever  frame  which  also  carries  the  tripper 
pulleys  for  the  belt.  When  the  flight  conveyor  is  inclined  at  the  angle  at 
which  the  material  naturally  piles,  a  high  pile  can  be  formed,  the  volume 
depending  on  the  length  of  the  belt  conveyor  and  the  length  of  the  flight 
conveyor. 

Stuart  Devices. — Several  patents  granted  to  F.  L.  Stuart  since  1916 
show  means  to  take  material  from  a  belt  conveyor  at  ground  level  and 
form  a  storage  pile  alongside  it.  Fig.  166  (patent  1331464  of  1920)  shows 


FIG.  166. — Forming  a  Pile  Alongside  a  Belt  Conveyor  by  Means  of  a  Suspended  Belt 
Taking  the  Discharge  from  the  Main  Conveyor. 

one  scheme.  The  conveyor  A  runs  through  a  wheeled  frame  which  is  in 
effect  a  high  tripper.  A  revolving  tower  mounted  on  power-driven  trucks 
moves  the  tripper  frame,  and  contains  a  pivoted  boom  which  carries  a  belt 
conveyor  that  receives  material  from  A.  Several  machines  of  this  design 
have  been  built  by  the  International  Conveyor  Corporation. 

An  adaptation  of  this  device  is  used  by  the  Baltimore  and  Ohio  Railroad 
at  Locust  Point,  Baltimore,  for  loading  cars.  The  tripper  frame  is  lower 
and  is  fitted  with  a  double-jointed  arm,  each  section  of  which  carries  a  short 
belt  conveyor  capable  of  270°  angular  movement.  In  a  manner  similar 
to  that  of  the  Manierre  loader  (Fig.  191),  the  conveyor  arm  can  be  inserted 
through  the  doorway  of  a  box  car  and  the  material  piled  at  either  end  of 
the  car. 

The  coal-shipping  pier  of  the  Baltimore  and  Ohio  Railroad  at  Curtis 
Bay,  Baltimore,  has  four  60-inch  12-ply  rubber  belt  conveyors  about 
1000-foot  centers  (see  Fig.  101)  which  discharge  coal  at  the  head  of  long 
inclined  loops,  which  are  practically  trippers,  to  reversible  shuttle  belts 
carried  by  traveling  towers  that  load  the  ships,  Fig.  167.  The  shuttle 
belts  can  be  racked  in  or  out  and  raised  or  lowered  to  suit  the  height  of 


SHUTTLE  CONVEYORS 


173 


ship's  freeboard  and  the  conditions  of  loading.  The  inclined  tripper  loop 
is  connected  to  the  frame  of  the  shuttle  belt  and  is  hinged  at  its  lower 
end  at  wharf  level,  so  that  the  l#ight  of  the  tripper  is  varied  to  suit  the 
elevation  of  the  shuttle  belt.  This  and  other  features  of  the  equipment 
of  this  pier  are  covered  by  Stuart's  patents  1192016  of  1916  and  1241053 
of  1917. 

At  the  coal  pier  of  the  Gulf,  Florida  and  Alabama  Railroad  at  Pensacola, 
Florida,  a  42-inch  belt  carrying  600  tons  run-of-mine  coal  per  hour  at  475 


FIG.  167. — Loading  Ships  by  Means  of  Shuttle  Belts  Serving  Longitudinal  Conveyors  on 

the  Wharf. 

feet  per  minute  loads  ships  through  a  chain  and  bucket  elevator  75  feet  high 
that  discharges  into  adjustable  chutes.  The  elevator  is  mounted  in  a 
power-driven  traveling  tower  which,  in  addition,  carries  the  loading  chutes 
and  a  pair  of  pulleys  which  act  as  a  tripper.  As  the  tower  travels  on  the 
pier,  the  coal  on  the  belt  is  discharged  into  the  foot  of  the  elevator. 

Shuttle  Conveyors. — In  some  places  where  the  discharge  is  spread  over 
a  comparatively  short  distance,  or  where  it  is  not  convenient  to  use  a  trip- 


Chain  &  Bucket 
Elevator 


FIG.  168. — Simple  Fo/m  of  Shuttle  Belt  Conveyor  Serving  Three  Pins. 


per,  it  is  possible  to  vary  the  point  of  discharge  by  using  a  belt  conveyor 
in  a  portable  frame,  so  that  the  conveyor  receives  material  at  various  points 
along  its  length,  but  always  discharges  over  the  end  pulley.  From  the  fact 
that  they  move  back  and  forth,  these  machines  are  called  shuttle  con- 
veyors. In  the  simple  form  shown  in  Fig.  168  the  shuttle  belt  i§  mounted 
in  a  short  frame  pushed  by  hand  so  that  the  discharge  over  the  end  pulley 
will  fall  into  bins  No.  1,  No.  2  or  No.  3,  while  a  by-pass  chute  from  the 


174 


DISCHARGING  FROM  THE  BELT 


head  of  the  elevator  discharges  into  No.  4.  This  device  does  what  might 
otherwise  be  done  with  a  fixed  conveyor  with  a  depressed  loading  end 
and  a  traveling  tripper  or  a  series  of  fixed  trippers;  in  some  places  it  is 
better  than  any  of  these  arrangements. 

Where  the  material  is  to  be  delivered  on  each  side  of  the  feed  point,  the 
belt  is  made  reversible  in  direction,  and  it  is  loaded  through  a  two-way 
chute  with  a  flap  gate  in  it.  In  this  way  it  is  possible  for  a  shuttle  conveyor 
of  length  L  to  discharge  over  a  length  of  pile  or  bin  nearly  equal  to  2L. 

The  original  shuttle  conveyor  patented  by  Bartlett  and  Overstrom  in 
1899  was  driven  and  propelled  by  a  rope  drive;  as  now  made,  the  conveyor 


plo'c^g  Shuttle  Celt  CoJvWor  30  Wide  Capacit^  125  T.P.H.  Belt  Spej, 


jZl-M > (^    ,., 27-0 >|<  370  ^    c.      ,         no  >K 

110  S'iLBelt  fccYeior_30  Wide  with  Chain  Oiling    Pniroll    Idlers  evorj  4  0    Spc.d  200  F.P.M. 


Capacity  125  T.P.H,         Crushed  Siturcinous  Coal     (  \1A' 


FIG.  169. — Long  Boiler  House  Served  by  Shuttle  Conveyor.     (Link-Belt  Company.) 


is  generally  driven  by  electric  motor.  When  the  frame  is  short,  or  seldom 
changed  in  position,  the  machine  is  moved  by  hand,  but  large  frames  are 
more  conveniently  propelled  by  a  separate  motor  or  by  a  rope  pulled  by  a 
winch-head  mounted  on  the  machine. 

In  Fig.  167  the  shuttle  frame  is  racked  in  and  out  by  power.  The 
reversible  belt  conveyor  in  it  receives  from  another  conveyor  running  the 
length  of  the  pier,  and  it  discharges  material  to  ships  lying  on  either  side 
of  the  pier.  All  the  motions  of  frame  and  conveyor  are  controlled  by  an 
operator  in  the  cabin  on  the  outboard  end  of  the  frame. 

Fig.  169  shows  a  boiler  house  served  by  an  elevator  which  stands  at 
what  will  be  the  middle  of  the  house  when  the  other  half  is  built.  A  shuttle 
conveyor  70  feet  long  serves  the  present  bin  which  is  104  feet  long.  When 
the  bin  is  doubled  in  length,  a  short  conveyor  similar  to  the  present  one  will 
run  to  the  left  of  the  elevator  and  from  the  end  of  it  the  present  shuttle 
conveyor  will  take  coal  for  delivery  to  the  new  bin.  In  this  way  a  70-foot 


SHUTTLE  CONVEYORS 


175 


176  DISCHARGING  FROM  THE  BELT 

shuttle  conveyor  will  serve  208  feet  of  bin.     Fig.  170  shows  the  side-view 
and  cross-section  of  the  conveyor  and  its  frame. 

When  the  full  length  of  a  shuttle  conveyor  is  always  over  a  bin  the  spill 
of  fine  material  from  the  return  belt  drops  into  the  bin,  but  when  a  part 
of  the  conveyor  extends  beyond  the  bin,  spill  of  fine  material  onto  the  floor 
below  may  be  objectionable.  In  such  a  case  a  belt  cleaner  or  brush  should 
be  used  at  one  or  both  ends  of  the  conveyor.  The  belt  shown  in  Fig.  170 
was  cleaned  by  a  wiper  at  each  end,  a  piece  of  rubber  belting  backed  up  by 
a  steel  strip  and  set  diagonally  under  the  return  run,  just  touching  the 
conveyor  belt.  It  was  adjustable  for  wear  and  was  simpler  than  a 
revolving  brush. 


CHAPTER  IX 


PROTECTING   AND    CLEANING   THE   BELT 


Material  Adhering  to  the  Belt. — When  coal,  coke,  clay  and  ores  are  han- 
dled particles  often  cling  to  the  belt  after  passing  the  discharge  point  and 
then  fall  off  on  the  return  run  on  meeting  the  idler  pulleys.  If  the  return 
idlers  are  close  to  a  floor  or  located  near  the  framing  of  a  bent,  as  in  Fig.  171, 
dirt  piles  up  so  as  to  prevent  the  pulley  from  turning;  the  belt  may  then 
wear  a  hole  in  the  rim  of  the  pulley  and  may  be  cut  and  perhaps  ruined. 
This  is  more  likely  to  happen  if  the  conveyor  is  enclosed  in  a  box-like  hous- 
ing, or  if  the  return  idlers  are  below  a  foot-walk,  hard  to  get  at,  and  hence 
the  grease  cups  are  not  filled  and  screwed  down  regularly.  It  often  happens, 


Door  Section 

at  each  Idler  witl 

Hinges  and 

Catches, 


o              o        /" 

,•) 

il    V 

1 

r 

%  Floor  Board 
Loose  at 

Idlers 


#20  Corrugated  Steel 


18  Belt  Conveyor 


%  Bolts 


22  Corrugate  1 


'3x3  Nailing 

Strip 

Counterbore 
for  Bolts 


FIG.  171.— Spill  of  Dirt  on 
Return  Run. 


FIG.  172. — Steel  Bridge  and  Enclosure  for  Belt 
Conveyor.    Housing  Open  on  the  Bottom. 


also,  that  the  return  run  is  hidden  from  view  by  the  protective  deck.  In 
Fig.  172  the  return  run  is  hidden  by  the  deck,  but  the  gallery  is  open 
under  the  return  belt  to  let  dirt  fall  '  away.  If  the  floor  cannot  be 
omitted,  there  should  be  plenty  of  space  below  the  return  belt  so  that  the 
spill  can  fall  clear  of  the  idlers  and  be  easily  seen  and  removed. 

For  the  same  reason,  it  is  well  to  set  return  idlers  in  relation  to  the 
framing  of  bents  and  the  travel  of  belt  so  that  the  dirt  falls  clear  of  the  bent, 
as  if  the  belt  shown  in  Fig.  183  ran  in  the  opposite  direction. 

Cleaning  Devices. — In  many  cases  the  dribble  of  material  along  the 
return  run  of  a  belt  conveyor  is  not  serious,  but  in  other  cases  it  is  so  objec- 
tionable that  a  cleaning  device  must  be  used  near  the  head  pulley  to  remove 
clinging  particles  from  the  belt.  It  is  also  necessary  to  clean  the  belt 
when  snub  pulleys  or  bend  pulleys  or  tandem-drive  pulleys  make  contact 

177 


178 


PROTECTING  AND  CLEANING  THE  BELT 


with  the  dirty  side  of  the  belt  on  the  return  run;  it  not  only  prevents 
particles  from  being  forced  into  the  belt  by  the  pulleys,  but  it  also  prevents 
material  from  accumulating  on  the  rims  of  the  pulleys  and  forming  crusts 
there  which  cause  the  belt  to  run  crooked,  or  perhaps  injure  it. 

Stationary  brushes  are  not  a  success  for  cleaning  belts;  they  fill  up 
with  dirt  and  fine  stuff  and  soon  become  useless.  Air  blasts  have  been 
used,  but  they  require  air  under  pressure,  and  the  cost  of  operation  is  great. 

Strips  of  belting  set  di- 
agonally against  the  under 
side  of  the  return  belt  have 
been  satisfactory  on  some 
belts  handling  coal. 

Revolving  Brushes. — A 
revolving  brush  (Fig.  173) 
consists  of  bunches  of  rattan 
or  fiber  splints  glued  into 
holes  drilled  in  a  wooden 
cylinder.  Fig.  174  shows 
one  with  its  drive ;  it  must  be 
set  so  that  when  the  loaded 

conveyor  is  started  at  slow  speed,  the  material  falling  vertically  from  the 
head  pulley  will  not  hit  the  brush.  A  chute  to  collect  the  scatter  and  spill 
back  of  the  brush  is  not  always  necessary  and  should  be  avoided  if  possible, 


FIG.  173. — Revolving  Brush  for  Cleaning  the  Belt. 


Position  of 

:i  aud  finite 
Chute  Filled  up  with  fine  Coal 


FIG.   174. — Head  of  Belt  Conveyor  and 
Drive  for  Cleaning  Brush. 


FIG.   175. — Right  and  Wrong  Positions  of 
Cleaning  Brush  and  Drip  Chute. 


but  when  it  is  used,  the  angle  must  be  steep  enough  to  let  damp  or  sluggish 
material  flow  readily  and  there  should  be  room  enough  between  brush  and 
chute  to  avoid  clogging.  Fig.  175  shows  a  24-inch  belt  discharging  crushed 
coal  to  a  grab-bucket  pit.  In  its  first  position  the  chute  clogged;  when  the 
brush  was  moved  forward  and  the  chute  was  made  steeper  it  worked  well. 

Speed  of  Brushes. — To  be  effective,  a  brush  must  work  against  the 
travel  of  the  belt  and  at  a  speed  sufficient  to  throw  the  fine  stuff  out  of  the 
bristles  and  keep  the  brush  clean.  Some  brushes  which  do  not  work  well 
have  the  bristles  or  bunches  of  splints  set  too  close  together  or  they  are 


BELT  CLEANERS  179 

run  at  speeds  that  are  too  low.     The  speeds  in  feet  per  minute  at  the  tips 
of  the  bristles  should  be,  for  brushes  8  to  12  inches  in  diameter: 

* 

Dry  materials .  .  .  .*. 800  to  1000  feet  per  minute. 

Damp  materials 1000  to  1200  feet  per  minute. 

Wet  and  sticky  materials 1200  to  1500  feet  per  minute. 

The  brush  should  be  mounted  so  that  it  can  be  adjusted  toward  the 
belt  to  compensate  for  wear  on  the  tips  of  the  bristles  and  in  such  a  way 
that  the  drive  to  the  brush  is  not  affected  (see  Fig.  174).  A  revolving 
brush  does  proper  work  only  when  it  is  kept  in  proper  adjustment  toward 
the  belt.  On  that  account  and  because  at  the  high  speed  necessary  brushes 
are  often  short-lived,  some  users  of  belt  conveyors  do  not  employ  them, 
but  let  the  dirt  fall  away  from  the  belt  and  then  clean  it  up  regularly. 

Other  Belt  Cleaners. — Since  it  is  not  easy  to  repair  a  fiber  brush  with 
the  materials  and  labor  ordinarily  available  a  number  of  substitutes  have 
been  used.  Ridgway,  in  1912,  patented  a  belt  beater  which  consists  of  a 
shaft  carrying  several  pivoted  arms  on  which  are  loosely  mounted  pipes 
extending  across  the  belt.  Under  the  action  of  centrifugal  force,  the 
arms  assume  a  radial  position  and  the  pipes  strike  a  glancing  blow  against 
the  belt.  It  was  designed  to  work  under  a  free  stretch  of  belt,  not  against 
a  belt  in  contact  with  a  pulley.  It  is  not  in  use  now. 

Fig.  176  shows  a  belt  flapper  which  has  some  resemblance  to  Ridgway's 
device.  It  is  a  wood  cylinder  to  which 
four  or  five  strips  of  old  belt  are 
screwed.  It  is  cheap,  easily  made  and 
readily  repaired ;  it  is  to  some  extent 
self-adjusting  and  will  clear  itself  of 
fine  stuff  at  speeds  less  than  those 
given  for  bristle  brushes.  The  outer 
edges  of  the  strips  are  sometimes 
weighted  by  steel  flats.  The  Winters 
patent  of  1920  covers  a  belt  cleaner 

with  rubber  strips  similar  to  Fig.  176  Fm  176._Rotary  Flapper  to  clean  a  Belt, 
but  mounted  beneath  the  return  belt 

on  a  frame  with  screw  adjustment  horizontally  and  vertically.  The 
vertical  adjustment  compensates  for  wear  on  the  edges  of  the  strips  and  the 
other  permits  the  drive  from  the  conveyor  head  shaft  to  be  kept  at  the 
proper  length  center  to  center. 

Other  belt  cleaners  have  been  used  experimentally.  One  is  a  repair 
for  an  ordinary  brush;  when  the  rattan  bristles  wore  out,  they  were  replaced 
by  strips  of  old  belt  bent  in  U  form  and  screwed  to  the  wooden  cylinder 
in  a  helix  (spiral)  of  rapid  pitch  so  that  two  or  three  of  the  edges  of  the 
strips  were  always  in  contact  with  the  belt.  Another  scheme  consists  of 
disks  of  old  belting  12  inches  in  diameter  strung  on  a  shaft  at  a  slight  angle 
and  nailed  to  oblique  sections  of  a  wood  cylinder  which  support  the  disks 


180  PROTECTING  AND  CLEANING  THE  BELT 

and  act  as  spacers.  This  is  said  to  work  by  frictional  contact  with  the 
belt  and  to  outlast  three  ordinary  rattan  brushes,  but  like  many  other 
"  kinks  "  it  is  apt  to  work  better  for  the  inventor  than  for  anyone  else. 

The  Carr  patent  of  1920  covers  a  method  to  remove,  from  the  return 
run  of  a  belt  conveyor,  wet,  sticky  material  like  cement  mortar.  The  return 
belt  is  kept  tight  and  by  means  of  a  revolving  cam-shaped  roller  pressing 
down  on  it,  the  belt  is  caused  to  whip  or  snap  violently  and  shake  off  the 
adhering  particles. 

Sprays  of  water  have  been  used  with  success  to  clean  belts  handling  wet 
concrete. 

The  idea  of  cleaning  a  belt  by  leading  the  return  run  across  a  wide  nozzle 
which  forms  the  inlet  of  a  vacuum  cleaner  is  disclosed  in  the  Bemis  patent 
of  1918.  It  is  designed  to  remove  dust  and  dirt  from  the  canvas  belts  used 
for  carrying  packages  in  stores. 

Tripper  Brushes. — Trippers  that  handle  sharp,  wet  material  like  sand 
or  crushed  ores  should  have  a  brush  just  ahead  of  the  lower  pulley  to  prevent 


Beet  Rod  Acting  aeT     Weight 
Fulcrum  and  Level 

FIG.  177. — Pulley  Rims  Kept  Clean  FIG.  178. — Scraper  for  Pulley  Rim 

by  Use  of  a  Scraper.  Combined  with  a  Deflection. 

sharp  particles  from  being  forced  into  the  belt  or  its  cover  on  the  reverse 
bend. 

Cleaning  Pulley  Rims. — It  is  sometimes  necessary  to  use  steel  scrapers 
on  the  rims  of  snub  pulleys,  tripper  pulleys  and  deflector  pulleys  in  order 
to  prevent  the  accumulation  of  material  which  might  hurt  the  surface  of 
the  belt  or  cause  it  to  run  out  of  line.  Fig.  177  shows  a  scraper  fitted  to 
a  weighted  lever  and  Fig.  178  illustrates  a  deflector  to  shed  the  scrapings 
clear  of  a  lower  run  of  belt. 

Protective  Deck. — In  order  to  prevent  scattered  material  from  dropping 
onto  the  return  belt  it  is  advisable  in  most  cases  to  cover  the  space  between 
the  conveyor  stringers  by  a  floor  or  deck  of  plank  or  light  sheet  steel.  Fig. 
172  shows  such  a  deck  in  cross-section  (see  also  Fig.  163).  It  lessens  the 
risk  that  lumps  of  material  or  sticks  or  tools  or  similar  things  falling  on  the 
return  belt  may  be  carried  between  the  foot  pulley  and  the  belt  and  perhaps 
tear  it  or  punch  a  hole  in  it.  On  the  other  hand,  it  affords  a  lodging  place 
for  dirt,  and  on  inclined  conveyors,  lumps  falling  on  the  deck  may  lodge 
against  the  idler  pulleys  in  such  a  way  as  to  form  a  very  effective  brake 
to  prevent  rotation.  In  Fig.  163  a  guard  has  been  placed  across  the  deck 
to  prevent  spill  from  jamming  against  the  hump  pulley. 


BELT  CONVEYOR  ENCLOSURES 


181 


The  deck  may  be  omitted  frqm"  conveyors  that  carry  only  fine  material 
and  from  inclined  conveyors  wherej}here  is  a  tandem  drive  or  a  bend  pulley 
near  the  lower  end  of  the  return  run.  At  such  places  the  lumps  can  be 
deflected  or  thrown  off  the  belt  without  doing  any  damage. 

When  belt  conveyors  are  mounted  on  elevated  frames  or  bridges,  or 
enclosed  in  housings,  the  deck  is  sometimes  objectionable  because  it  covers 
up  the  lower  run  out  of  sight  and  hinders  or  prevents  access  to  the  bearings 
of  return  idlers.  In  such  cases,  if  the  conveyor  belt  is  plenty  wide  enough 
and  not  likely  to  spill  over  the  sides,  the  deck  may  be  omitted  and  a  wiper 
or  plow  used  over  the  return  belt  near  the  foot  to  push  off  any  stray  piece 
before  it  comes  to  the  pulley.  Doing  this  is,  of  course,  choosing  between 
two  evils;  the  right  way  is  to  use  a  deck  and  place  the  conveyor  stringers 
so  that  the  return  belt  is  visible  for  inspection  (see  Fig.  182). 

In  some  cases  where  belts  are  loaded  at  a  number  of  places  along  their 
length  as  on  coke  wharves  at 

by-product    plants,  a   deck  does         ^ »**«m<ssL,.  ^ 

not  afford  complete  protection 
against  lumps  getting  on  the 
return  belt  and  is  a  place  where 
coke  may  lodge  and  do  damage. 
At  one  plant  the  return  belt  was 

run  over  two  trinner  nullevs  near   FlG-  179'~ TriPPer  Device  to  Remove  Lumps 
run  over  from  Return  Run  of  Belt      (R    H   Beau_ 

the  foot   wheel.      This   put   two       mont  Co.) 

extra  bends   in   the  belt  but  it 

prevented  lumps  of  coke  from  being  jammed  between  the  belt  and  the  foot 

pulley,  and  it  gathered  the  spill  at  one  place  convenient  for  removal  (Fig. 

179).     There  was  no  deck  over  the  lower  run  in  this  case. 

Belt  Conveyor  Enclosures. — When  a  belt  conveyor  runs  outdoors 
throughout  all  its  length,  or  from  one  building  to  another,  it  may  be  necessary 
to  cover  it  for  several  reasons:  (1)  To  avoid  exposure  to  sunlight,  rain  or 
snow;  sunlight  is  injurious  to  rubber  (see  p.  44) ;  the  material  carried  on  the 
belt  may  be  damaged  if  wet,  or  the  belt  may  carry  water  into  a  building 
or  into  a  bin  and  create  a  nuisance.  (2)  To  avoid  exposure  to  wind;  a 
strong  wind  may  blow  material  off  the  belt  or  may  lift  the  belt  off  the  idlers 
or  cause  it  to  run  crooked. 

The  simplest  enclosure  is  merely  a  roof  over  the  conveyor,  with  the  sides 
left  open.  This  construction  on  an  open  wood  deck-bridge  is  similar  to 
that  shown  in  Fig.  180.  The  roof  is  made  of  corrugated  steel  sheets  screwed 
on,  and  the  dimension  A  is  made  about  18  inches  so  that  when  the  sides 
are  left  open  a  man  can  reach  in  under  the  roof  to  the  grease  cups  of  the 
troughing  idlers  on  both  sides  of  the  conveyor.  The  return  idler  pulleys 
in  this  design  run  loose  on  the  shaft  and  are  lubricated  from  one  large  cup 
on  the  footwalk  side.  When  sides  are  added,  the  sheathing  on  the  foot- 
walk  side  is  held  on  by  bolts  with  thumb-nuts;  that  on  the  far  side  is  nailed 
on.  Over  each  troughing  idler  there  is  a  removable  door  in  the  roof  sheath- 
ing about  24  inches  wide,  to  give  access  to  the  grease  cups  of  the  troughing 


182 


PROTECTING  AND  CLEANING  THE  BELT 


idlers  and  dimension   A    is  made  about   12   inches  to  avoid  too  long  a 

reach. 

Fig.  172  shows  a  steel  deck-bridge  with  two  footwalks  that  give  access 

to  bearings  on  both  sides 
through  hinged  doors  in  the 
corrugated  sheathing  opposite 
each  idler.  Bearings  for  re- 
turn idlers  are  reached  by 
removing  loose  boards  from 
the  decking  above  the  lower 
run>  but  in  this  design,  as  in 


8x4  Blockkq  12  Lg. 


3x6   G-OCtoC=A 


Blocking  to  Raise  Grease  Cup  AbOTe 

Foot  Walk  and  Prevent  Belt  from. 

Rubbing  or,  Cr.,33  Piece  "A" 


Oj 


1   O 


ol 


!o 


-Trmss  Rods" 


return  belt  and  its  idlers  are 
practically  concealed  from 
view.  This  is  always  an  ob- 
jection; if  an  idler  pulley  sticks 
and  refuses  to  turn,  it  may 
damage  the  belt  if  it  is  not 
detected  promptly. 

Fig.  181  shows  an  18-inch 
belt   conveyor   enclosed   in   a 
through-bridge.   The  structure 
was  made  wide   enough  for  a 
tripper,  but  there  was  a  foot- 
walk  on  one  side  only  and  it 
was  not  easy  to  get  at  the  far 
side  of  the  tripper  for  lubrica- 
FIG.  180.—  Enclosure  for  Belt  Conveyor,  Corrugated    tion  and  the  necessary  inspec- 
Steel  on  Wood  Frame.     (R.  H.  Beaumont  Co.)  ,.  JA 

tion  and  attention.     Another 

defect  in  the  design  is  that  the  return  run  is  completely  covered.  It  is  hard 
to  get  at  the  bearings  and  the  belt  can  be  seen  only  by  unbolting  and 
removing  sections  of  the  steel  deck. 

A  design  better  in  both  respects  is  illustrated  in  Fig.  182.  Both  sides 
of  the  conveyor  are  accessible  for  inspection  and  lubrication,  and  the 
return  belt  can  be  seen  on  both  top  and  bottom  for  its  full  length.  The 
bridge  is  open  below  the  return  run  so  that  dirt  falls  away  clear  of  the 
conveyor,  and  if  any  does  lodge  on  the  lower  bracing  of  the  bridge,  it  cannot 
foul  the  return  idlers  and  prevent  them  from  turning  (see  Fig.  171). 

A  belt-conveyor  housing  used  by  the  Stephens-Adamson  Manufacturing 
Co.  on  open  deck  bridges  is  in  section  an  inverted  U,  open  at  the  bottom 
and  wide  enough  to  cover  the  belt,  the  idlers  and  the  stringers  on  which 
they  are  mounted.  One  panel-length  of  housing  covers  two  troughing 
idlers;  transverse  slots  in  the  rounded  top  provided  with  doors  give 
access  to  the  idlers  for  examination  and  lubrication. 

It  is  worthwhile  to  emphasize  the  statement  that  when  belts  handle 
coal,  coke  and  other  substances  which  are  regularly  or  at  times  moist,  some 


BELT  CONVEYOR  ENCLOSURES 


183 


of  the  fine  particles  cling  to  the  belt  and  are  dropped  off  at  each  idler  on 
the  return  run,  most  of  them  near  the  discharge  end,  but  often  at  each  idler 
back  to  the  loading  point.  This^pill  is  often  a  serious  matter,  and  if  it 
cannot  be  allowed  to  fall  freely  away  at  each  idler,  the  supporting  structure 


#  20  Corrugated  Steel 


FIG.  1£1. — Defective  Design  of  Steel         FIG.   182. — Bridge  and  Supports  for  Belt  Con- 
Bridge  and  Belt  Supports.  veyor.     Both  Runs  Visible  and  Accessible. 

or  enclosure  should  be  designed  so  that  the  spill  can  be  removed  regularly 
and  easily. 

Enclosures  which  are  designed  chiefly  for  architectural  effect  and  neat  and 
trim  appearance  often  cause  trouble  and  expense,  because  they  confine  the 
spill  and  hinder  inspection  and  cleaning. 


CHAPTER  X 


PACKAGE  CONVEYORS 


Package  Conveying. — The  belt  is  generally  the  cheapest  and  best  con- 
veyor for  packages  of  light  weight,  papers,  books,  wrapped  goods,  sacks, 
bags,  and  for  boxes  that  are  not  too  heavy.  The  belts  are  always  run  flat. 
Belts  for  Package  Conveyors. — Since  the  work  is  usually  dry  and 
indoors,  and  the  material  not  harmful  to  the  surface  of  the  belt,  it  is  not 
necessary  to  use  a  belt  with  a  high  resistance  to  abrasion  and  to  the  action 
of  water.  Many  package  conveyors  that  carry  light  goods  use  solid-woven 
belts  (see  p.  50)  of  a  thickness  corresponding  to  4-ply.  If  the  length  is  short, 
the  belts  may  be  used  just  as  they  are  woven,  without  waterproofing  to 
resist  atmospheric  moisture;  they  are  cheap,  clean,  and  contain  nothing  to 
mark  or  stain  the  goods  carried.  Such  belts  are  very  flexible  and  wfll  bend 
readily  over  the  8-inch  end  pulleys  and  the  2 i -inch  idlers  generally  used  in 
such  conveyors.  In  longer  conveyors  where  the  stretch  of  an  untreated 
belt  is  objectionable,  fabric  belts  (solid  woven  or  built-up)  may  be  treated 
with  a  colorless  Class, 3  compound  (see  p.  48).  This  is  clean,  and  leaves 
the  belt  quite  flexible.  Belts  for  handling  baskets,  boxes,  heavy  parcels, 

mail  bags,  express  matter,  etc.,  need  a 
density  of  bocjy  and  a  surface  tough- 
ness to  resist  the  bumps,  blows  and 
scratches  caused  by  sharp  corners, 
nails  and  metal  fastenings.  They  are 
frequently  stitched  canvas  belts  with 
Class  1  impregnation  (see  p.  48),  not 
so  flexible  as  those  treated  with 
Class  3  compounds,  but  more  resistant 
to  wear.  Fig.  183  shows  one  of  many 
such  belts  used  in  a  Chicago  mail- 
order house.  Table  9,  page  53,  gives 
a  comparison  between  two  specimens 
of  solid-woven  belt  and  one  stitched 
canvas  belt  as  to  stretch  and  ultimate 
strength. 

Package  conveying  does  not  often 
require  a  belt  with  a  minimum 
amount  of  stretch  or  a  maximum  resistance  to  moisture;  hence  rubber  belts 
and  balata  belts  are  not  often  used  for  this  work  unless  their  prices  are 

184 


FIG.  183.  —  Stitched  Canvas  Belt  for 
Assembling  Goods  on  Mail-orders. 
(Imperial  Belting  Co.) 


SUPPORTING  ROLLS  FOR  PACKAGE  CONVEYORS 


185 


low  enough  to  compete  with  solid-woven  or  stitched  belts.  When  rubber 
belts  are  used  a  cover  is  seldom*  needed,  experience  showing  that  friction 
surface  belts  resist  the  wear  sumcie&tly  well  and  that  cheaper  belts  are  more 
economical  in  the  long  run. 

Supporting  Rolls  for  Package  Conveyors. — Wood  rolls  are  apt  to  warp, 
crack  and  get  out  of  balance;  they  are  practically  obsolete.  Steel  rolls 
in  sizes  4  inches  and  larger  are  generally  made  of  steel  pipe  or  tubing  shrunk 
onto  cast-iron  heads  in  which  are  inserted  shafts,  either  as  short  stub  ends 


-Width  of  Belt +3 
Width  of  Belt-|4i" 


Hardwood  Bearing 
Impregnated  with  Oil 


Stamped  Steel  Hoad 
Welded  to  Tubing 


Return  Rolls  Spaced  about  6  Feet 

FIG.  184. — Package  Conveyor,  Wood  Frame  and  Oiiless  Bearings.     t.Lamson  Co.) 

or  "  gudgeons  "  cast  with  the  heads  or  set  screwed  in  place,  or  as  shafts 
extending  through  both  heads  with  projection  enough  for  a  bearing  at  each 
end.  For  light  belts,  it  is  important  to  have  a  roll  that  is  light,  lively, 
and  accurate  in  balance;  most  of  them  for  store  service  are  made  of  2^-inch 
diameter  steel  tubing.  If  stub-end  shafts  are  used,  the  cast-iron  heads 
must  be  of  sufficient  length  to  maintain  the  tube  and  the  two  end  shafts 
in  permanent  alignment  (see  Fig.  186).  If  a  through  shaft  is  used,  the 
heads  may  be  much  lighter,  but  the  shaft  must  be  perfectly  straight  (see 
Fig.  184). 

Most  package  conveyors  are  used  indoors  and  in  places  where  neatness 


186 


PACKAGE  CONVEYORS 


and  compactness  are  of  some  importance.  Fig.  184  shows  a  cross-section 
of  both  runs  of  belt  conveyors  from  6  to  48  inches  in  width,  all  contained 
within  the  depth  of  a  11-inch  plank  side.  The  edges  of  the  belt  overhang 
the  ends  of  the  rolls  by  1J  inches,  but  are  prevented  from  sagging  too  far 

and  dropping  goods  by  a  wood  guard 
strip  which  is  continuous  for  the 
length  of  the  conveyor  except  for 
clearance  at  the  bearings.  Fig.  185 
shows  a  similar  construction  used 
for  packages  in  stores  where  the 
conveyor  is  hung  from  the  ceiling  by 
rods,  and  where  for  the  sake  of  ap- 
pearance it  is  enclosed  on  sides, 
bottoms  and  ends  with  wood  con- 
struction and  wall-board  panels.  The 
bearings  shown  in  Fig.  184  are  hard 
wood  blocks  impregnated  with  a 
Wal1  B°Vard  lubricant  and  held  in  a  yoke  which 

FIG.  185.— Package  Conveyor,  Panel  Board     allows  them  some  freedom  of  move- 
Enclosure.    Bronze  Roll  Bearings.    (Lam-  ,        0      ,    ,  .  ., 
son  Co.)                                                      ment.     Such  bearings  require  no  oil; 

they    are    sufficient    for    moderate 

loads.  The  bearings  shown  in  Fig.  185  are  bronze,  mounted  in  cast-iron 
holders  in  such  a  way  as  to  maintain  alignment  with  the  roll  shafts. 

Fig.  186  illustrates  a  42-inch  belt  conveyor  with  all  steel  construction; 


FIG.  186. — 42-inch  Belt  Conveyor  for  Department  Store  Service.     (Link-Belt  Company.) 

the  shaft  bearings  are  spherical  balls  of  Babbitt  metal  cast  with  a  central 
chamber  in  which  is  fitted  a  felt  washer  to  retain  oil  for  lubrication. 

Other  Forms  of  Package  Conveyors. — Bulletins  of  manufacturers  show 
package  conveyors  with  the  belt  supported  on  one  or  both  runs  by  oiled 
wood  strips  instead  of  rolls;  conveyors  with  upper  run  and  lower  run 
spaced  apart  so  that  they  can  be  loaded  with  goods  on  both  runs  for  move- 


CAPACITIES  OF  PACKAGE  BELTS 


187 


ment  in  either  direction;  conveyors  for  trays  where  the  belts  are  carried  on 
rolls  set  close  together.  > 

Capacities  of  Belts  in  package  conveyors  are  much  less,  measured  in 
pounds,  than  the  corresponding  capacities  in  handling  bulk  materials. 
The  service  is  generally  intermittent,  the  goods  are  usually  placed  on  by 
hand,  the  speed  is  low — 75  to  150  feet  per  minute,  and  the  width  is  often 
determined  by  the  dimensions  of  the  packages  rather  than  by  the  quantity 
to  be  handled.  The  rate  at  which  the  packages  can  be  taken  away  at  the 
discharge  point  will  sometimes  determine  the  carrying  capacity  of  a  belt. 

Discharge  is  generally  over  the  end  pulley  or  by  means  of  scrapers  at 


36  Belt  75  ft.per  min. 


XB  Head  Pulley 

/Cut  Gears  in  Qfl  B« 


SECTION  A-A 


FIG.   187. — Transfer  Between  Two  Package  Conveyors.     (Link-Belt  Company.) 

intermediate  points.  A  typical  transfer  between  two  package  conveyors 
in  a  department  store  is  shown  in  Fig.  187.  The  head  pulley  is  8  inches 
in  diameter;  it  is  placed  quite  close  to  the  receiving  belt  with  merely  a 
guard  to  bridge  the  few  inches  of  gap.  This  short  connection  saves  height, 
lessens  the  chance  of  breakage  of  goods  and  prevents  an  accumulation  at 
the  transfer  point.  In  transferring  sacks  and  bulky  packages,  it  is  better 
to  place  the  receiving  belt  lower,  so  that  the  package  has  more  drop  and  will 
be  taken  away  promptly;  otherwise  it  may  hang  between  the  two  con- 
veyors and  be  rubbed  and  perhaps  torn  by  the  moving  belts. 


CHAPTER  XI 


SPECIAL  USES  OF  BELT  CONVEYORS 

Special  Machines  Using  Belt  Conveyors. — Within  the  past  ten  years  a 
number  of  portable  belt-conveyor  machines  have  come  into  use  for  loading 
and  unloading  cars,  piling  bulk  material  into  storage  or  reclaiming  from 
storage  and  doing  similar  work  formerly  done  by  human  muscle  with 
shovel  and  wheelbarrow.  In  order  that  these  machines  can  be  easily  handled 
and  moved  from  place  to  place  the  frames  are  made  as  light  as  possible  and 
the  conveying  apparatus  and  the  driving  machinery  have  been  designed 
especially  to  be  compact  and  without  superfluous  weight. 

The  portable  conveyor  made  in  several  styles  by  the  Barber-Greene  Co. 
of  Aurora,  111.,  consists  of  a  standard  discharge  end,  a  standard  drive  end 
with  a  loading  hopper  and  an  electric  motor  and  standard  intermediate 


FIG.  188.— Portable  Steel-frame  Belt  Conveyor.     (Barber-Greene  Co.) 

sections  (Fig.  188).  When  the  two  end  sections  are  coupled  together  and 
mounted  on  a  pair  of  wheels  they  make  a  portable  machine  15  feet  long. 
The  intermediate  sections  are  made  in  lengths  of  3,  6,  9,  12  or  15  feet; 
where  these  are  inserted  between  the  standard  end  sections  they  make 
portable  machines  of  various  lengths  up  to  60  feet.  The  belts  are  12,  18, 
24  or  30  inches  wide,  and  run  over  three-pulley  idlers  set  at  30°  troughing. 
The  pulleys  are  made  of  steel  tubing. 

The  Scoop  Loader  (Wentz  reissue  patent  of  1920),  made  by  the  Portable 
Machinery  Co.  of  Passaic,  N.  J.,  is  especially  light  and  portable.  The  belt- 
is  12  or  16  inches  wide  and  has  cleats  or  flights  to  prevent  material  from 

188 


THE  SCOOP  LOADER 


189 


slipping  back ;  it  runs  flat  between  continuous  skirt-boards  with  most  of  the 
weight  carried  on  small  rollers^  but  with  its  edges  supported  on  wood 
stringers  (Fig.  189).  The  loweg,end  of  the  frame  is  brought  to  a  sharp 
point  and  has  a  small  belt  pulley  set  very  low  so  that  the  foot  of  the  machine 


TVood  Rollers 

to  Support 

.Middle  of  Belt 


Shoe  Plate 


Sharp  Corner  to  Force  into  Material 

LONGITUDINAL  SECTION 


CROSS   SECTION 

FIG.  189. — "Scoop"  Loader,  Bottom  end  and  Cross-section.     (Portable  Machinery  Co.) 

can  be  forced  into  a  pile  of  material  and  pick  up  its  load  without  much 
shoveling.  Judged  by  usual  belt-conveyor  standards,  the  pick-up  of 
material  is  bad  and  the  support  of  the  belt  inferior;  but  in  the  service  for 
which  the  machine  is  generally  sold,  the  work  is  intermittent  or  occasional, 


FIG.  190.— Pratt  Loader  Piling  Sand  in  Box-car.     (Link-Belt  Co.) 

and  the  belt  lasts  long  enough  to  show  a  low  cost  per  ton  of  material  handled. 
The  wear  on  the  belt  is  often  a  minor  consideration  in  machines  of  this 
general  class ,  they  enable  one  man  to  do  the  work  which  formerly  took  two 
or  three;  they  do  the  work  more  quickly,  reduce  charges  for  car  demurrage 
and  often  increase  the  available  storage  capacity  of  a  yard  or  a  shed.  To 


190  SPECIAL  USES  OF  BELT  CONVEYORS 

get  these  advantages  with  simplicity  of  construction  and  ease  of  handling  the 
machines  it  may  be  true  economy  to  let  belts  wear  out  rapidly. 

The  Pratt  Loader  (Fig.  190)  (Link-Belt  Company,  Philadelphia)  is  a 
short  belt  conveyor  mounted  on  a  light  wheeled  frame  and  run  so  fast 
that  it  throws  the  material  far  beyond  the  end  of  the  machine.  A  machine 
standing  in  the  doorway  of  a  box  car  can  pile  material  high  at  the  ends  of 
the  car.  The  belt  is  fitted  with  cleats  and  slides  at  500  feet  or  1000  feet 
per  minute  over  a  steel  bottom  plate  between  continuous  skirt-boards  on 
the  upper  run.  Naturally  the  belt  does  not  last  so  long  as  it  would  in  an 
ordinary  belt  conveyor,  but  as  has  been  said  above,  the  durability  of  the 
belt  is  subordinated  to  other  considerations  in  apparatus  of  this  kind. 

The  Manierre  Loader  (Manierre  Engineering  and  Machinery  Co.,  Mil- 
waukee) is  a  belt  conveyor  mounted  on  a  steel  frame  hinged  at  several  points 
so  that  it  will  swing  into  a  box  car  through  the  doorway.  The  conveyor 
does  not  run  fast;  it  is  adjustable  for  angle  and  will  pile  material  into  the 
ends  of  the  car  without  breakage,  starting  with  the  delivery  end  close  to 


FIG.   191. — Manierre  Loader  Receiving  from  Belt  Conveyor  and  Delivering  to  Box-car. 

the  floor  and  raising  as  the  pile  forms.  It  is  used  chiefly  for  material  like 
coal  and  coke  which  must  be  handled  without  unnecessary  breakage 
(Fig.  191). 

Distributing  Coal  in  Holds  of  Ships. — At  shipping  piers  at  Greenwich 
Point,  Philadelphia,  Curtis  Bay  and  Port  Covington,  Baltimore  and  else- 
where, coal  is  distributed  in  the  holds  of  ships  away  from  hatches  and 
close  up  under  decks  by  means  of  high-speed  belts  attached  to  the  lower 
end  of  telescopic  chutes  (see  Fig.  167).  These  belts  are  36  or  48  inches  wide, 
run  at  2500  or  2700  feet  per  minute  over  pulleys  12  or  18  inches  in  diameter 
set  about  4  feet  apart  and  threw  the  coal  30  or  40  feet  beyond  the  machine 
at  the  rate  of  a  carload  (50  tons)  in  two  or  three  minutes.  Fig.  192  shows 
the  assembled  lower  end  of  the  telescopic  chute  with  men  putting  on  a  new 
belt.  The  belts  are  usually  8-ply  rubber  or  balata  belts  with  strips  of  the 
same  material  about  U  inches  wide  riveted  across  the  carrying  surface 
every  6  inches  and  with  similar  pieces  riveted  along  the  margins  to  take 
the  edge  wear.  At  the  very  high  speed,  the  abrasion  of  the  carrying  surface 
is  severe  and  rapid,  rubber  covers  do  not  last  long  and  the  life  of  the  belt 


CONVEYING  BETWEEN  TWO  BELTS  191 

is  determined  by  the  rate  at  which  it  is  weakened  by  the  destruction  of 
its  plies  of  fabric.  A  canvas* or  balata  belt  with  a  heavy  close-woven 
duck  does  not  give  quite  the  service  of  a  high-grade  rubber  belt  with  a 
thick  cover,  but  it  is  sold  at  a  lower  price  and  in  some  instances  carries 
enough  coal  to  make  it  more  economical  than  the  rubber  belt.  Good 
balata  belts  carry  about  30,000  tons  on  one  of  these  distributors;  expensive 
rubber  belts  do  not  average  40,000  tons.  This  represents  only  a  few 
days  or  weeks  of  life,  nevertheless  it  pays  to  wear  out  belts  at  $100  or  $200 
apiece  rather  than  employ  gangs  of  shovelers  to  trim  the  coal  in  the  cargo 
space  of  the  ships.  The  loading  is  done  better  and  in  much  less  time; 
and  the  ship  is  not  held  so  long  at  the  pier  and  out  of  carrying  service, 


FIG.  192. — Lower  End  of  Ship-loading  Chute  Fitted  with  High-speed  Belt  for  Trimming 

Coal  Under  Decks. 

Conveying  between  Two  Belts. — The  angle  at  which  a  belt  will  carry 
material  up  an  incline  is  limited  by  the  tendency  of  the  material  to  roll 
back  on  itself  or  slip  on  the  belt,  but  if  the  material  can  be  prevented  from 
doing  that,  it  can  be  carried  at  a  steeper  angle.  It  can  be  done  if  a  second 
belt  travels  along  with  the  conveyor  belt  with  slack  enough  to  lie  over 
and  confine  the  material. 

This  principle  has  been  used  in  agricultural  implements  to  elevate  straw, 
etc.,  and  even  to  carry  coal  in  inclined  belts  forming  part  of  loading  ma- 
chines, but  as  applied  to  bulk  materials  which  consist  of  a  mixture  of  lumps 
and  fine?,  the  hold  of  the  upper  belt  is  uncertain  and  some  of  the  material 


192 


SPECIAL  USES  OF  BELT  CONVEYORS 


may  slip  back  or  fall  out.  This  drawback  does  not  exist  to  the  same  degree 
with  packaged  goods,  and  when  the  pieces  carried  are  uniform  in  size  and 
not  too  thick,  like  newspapers,  there  is  no  difficulty  in  conveying  them  at 
angles  up  to  the  vertical. 

Newspaper  Conveyors  and  Elevators. — The  original  newspaper  conveyor 

of  this  type  (Perkins  patent,  1880)  is  shown 
in  Fig.  193.  By  confining  the  vertical  runs 
of  the  two  belts  A  and  B  between  pulleys 
set  opposite  or  staggered,  the  papers  are 
prevented  from  slipping  by  the  pressure  of 
the  belts  toward  each  other.  There  is, 
however,  one  objection  to  the  use  of  belts 
for  this  work,  when  the  machines  take 
papers  directly  from  the  press,  as  is  usually 
the  case.  The  ink  is  then  not  quite  dry  and 
will  be  smeared  or  smudged  if  the  belts 
absorb  the  ink  or  if  in  passing  over  the  pul- 
leys there  is  movement  between  the  belts 
and  the  papers.  In  the  most  recent  ma- 
chines of  this  type,  built  by  the  Lamson 
Company,  the  belts  have  been  replaced  by 
cotton  cords  wound  round  with  a  covering 
of  soft  iron  wire  (Cowley  patent,  1917).  The  wire  touches  the  papers  in 
small  spots  only  and  is  not  likely  to  smear  the  ink. 

The  same  principle  has  been  used  (Lamson  Co.)  in  a  machine  to  handle 
tin  crowns  or  bottle  caps.  The  caps  are  carried  between  two  belts  which 
are  grooved  (Fig.  194)  to  such  a  depth  that  when  the  belts  are  together, 


FIG.  193. — Elevating  Newspapers 
Between  Two  Belts. 


FIG.  195. — Conveying  Material  between 
Two-flanged  Belts. 


Convex  Guide 

FIG.  194.— Grooved  Belts  for  Elevating 
Small  Articles.  (Cross-section  of 
Vertical  Run.)  (Lamson  Co.) 

the  caps  will  be  squeezed  between  them.  On  the  vertical  run,  the  belts  are 
guided  over  a  surface  slightly  convex  so  as  to  keep  them  together  and  pre- 
vent the  caps  from  slipping. 

German  patent  52697  to  Luther  illustrates  the  same  idea  applied  to 
bulk  materials  (Fig.  195).  It  is  not  in  practical  use. 

The  Anderson  patent  of  1920  proposes  to  use  two  short  vertical  belts 
placed  under  the  hopper  of  a  molding  machine  as  a  means  to  draw  sand 
from  the  hopper  and  throw  it  forcibly  into  a  flask  or  sand-mold,  so  as  to 
pack  the  sand  and  lessen  the  labor  of  ramming. 


BELT  CONVEYING  BY  ROLLING  CONTACT 


193 


Belt  Conveying  by  Rolling  Contact. — The  Hopkins  and  Fellows  device 
(patented  1904)  used  in  can  factories  and  canneries  to  carry  and  elevate 
round  tin  cans  is  shown  in  Fig.  1$).  Cans  rolled 
down  the  guide  at  the  foot  of  the  machine  rest 
on  a  yielding  section  of  track  and  come  in  contact 
with  the  elevating  belt.  This  is  kept  under  ten- 
sion by  a  weighted  pulley  and  by  being  deflected 
from  a  straight  line  by  the  convex  curvature  of 
the  track  on  which  the  cans  roll.  The  motion  of 
the  belt  rolls  the  'cans  up  the  track  until  the  track 
ends  as  shown  in  the  figure,  or  the  track  may 
be  curved  with  a  flexible  section  around  the 
upper  pulley  to  return  the  cans  to  the  side  from 
which  they  came. 

Picking  or  Sorting  Belts. — When  belts  are  used 
to  expose  ores  or  minerals  to  the  inspection  of  men 
or  boys  who  remove  waste  material  from  them 
the  travel  must  be  slow,  generally  not  over  50 
feet  per  minute  and  even  less  if  the  material  is 
lumpy.  The  bed  of  material  should  be  thin  and 
wide  so  that  all  the  pieces  can  be  seen  and  can 
be  turned  over  without  too  much  exertion.  A 
belt  wider  than  48  inches  makes  the  pickers 
(boys  especially)  reach  too  far;  they  cannot  work 
so  well,  and  the  sorting  is  not  so  efficient  as  when 
the  belt  is  36  inches  wide. 

Capacity. — The  capacity  of  a  picking  belt  is 
an  indefinite  quantity,  but  it  is  always  less  than 
the  capacity  of  the  belt  calculated  as  a  conveyor 
for  its  particular  speed.     The  following  may  be  used  as  representing  the 
working  capacities  of  picking  belts  on  metalliferous  ores. 

Capacity  of  30-inch  belt  on  three-pulley  idler  with  broad  center  pulley 
in  cubic  feet  per  hour  =  l.3W2  at  50  feet  per  minute. 

Capacity  of  36-inch  belt  on  three-pulley  idler  with  broad  center  pulley 
in  cubic  feet  per  hour  =  1.1  W*  at  50  feet  per  minute. 

Capacity  of  42-inch  belt  on  three-pulley  idler  with  broad  center  pulley 
in  cubic  feet  per  hour  =  IWZ  at  50  feet  per  minute. 

Capacity  of  48-inch  belt  on  three-pulley  idler  with  broad  center  pulley 
in  cubic  feet  per  hour  =0.9TF2  at  50  feet  per  minute. 

Idlers  for  Picking  Belts. — Standard  three-pulley  or  five-pulley  idlers 
are  not  generally  used  for  this  work;  they  crowd  the  material  toward  the 
center  of  the  belt.  It  is  better  that  the  belt  should  run  nearly  flat  with  the 
material  spread  out  to  near  the  edges;  at  the  slow  speed  there  is  not  much 
tendency  for  the  pieces  to  roll  off.  Three-pulley  idlers  (see  Fig.  70)  with 
a  broad-face  center  pulley  are  listed  for  this  work  by  several  manufacturers ; 
they  spread  the  material  out  better  than  standard  idlers.  Spool  idlers 


FIG.  196.  —  Conveying  and 
Elevating  Tin  Cans  by 
Rolling  Contact. 


194 


SPECIAL  USES  OF  BELT  CONVEYORS 


(see  Fig.  84)  or  flat  rolls  with  occasional  concentrators  (see  Fig.  28)  can  also 
be  used. 

The  number  of  men  required  to  sort  or  pick  depends  upon  the  size  and 
weight  of  the  pieces  and  the  amount  of  material  to  be  removed  from  the  belt ; 
it  can  be  determined  only  by  a  test  under  operating  conditions.  Peele's 


FIG.   197. — Various  Arrangements  of  Picking  Bands  for  Disposal  of  the  Waste. 

Mining  Engineers'  Handbook,  1st  edition,  page  1651,  says  that  the  weight 
per  hour  picked  off  a  belt  in  1-inch  pieces  weighing  j  pound  is  about  one- 
fifth  the  weight  of  the  material  picked  off  in  6-inch  lumps  weighing  58 
pounds  and  that  the  maximum  is  attained  if  the  pieces  are  about  3  to  7 
pounds  weight. 

The  length  of  a  picking  belt  is  determined  by  the  number  of  pickers 


PICKING  BELTS  195 

and  by  the  space  alongside  allowed  for  each  one.  Thirty  to  40  inches  is 
usual  per  man  on  each  side  of  the^belt. 

The  incline  should  not  exceed  1Q°  or  12°  to  prevent  lumps  from  rolling 
on  the  belt  and  hurting  men's  hands.  Moreover,  men  cannot  stand  com- 
fortably on  an  incline;  if  the  belt  is  on  a  slope  it  may  be  better  to  build 
the  working  platform  as  a  series  of  steps;  for  a  10°  slope,  a  36-inch  tread 
has  a  6^-inch  rise. 

Disposal  of  the  Waste. — Fig.  197  (Schmitt's  Text  Book  of  .Rand  Metal- 
lurgic  Practice)  shows  four  methods.  The  scheme  of  Fig.  B  allows  two 
kinds  of  separation  to  be  made,  the  pickers  on  each  side  of  the  belt  picking 
off  one  grade  of  material  as  waste  or  for  re  treatment.  It  requires  the 
pickers  to  turn  around,  and  in  that  way  they  lose  time.  Fig.  C  is  a  common 
arrangement;  it  is  easy  to  drop  the  pickings  into  the  chute  boxes,  one  at 
each  man's  place,  and  the  main  belt  when  worn  can  be  cut  down  or  pieced 
to  make  the  lower  belt.  The  disadvantage  of  Fig.  D  is  that  the  discharge 
from  the  lower  run  requires  two  pulleys  to  be  arranged  as  a  tripper  near  the 
foot  similar  to  Fig.  179.  The  pulley  side  of  the  belt,  not  generally  protected 
by  a  cover,  is  apt  to  be  injured  by  particles  of  rock  adhering  to  it  and 
forced  into  the  fabric  by  contact  with  the  pulleys. 

In  South  African  practice  the  work  on  the  picking  belts  is  very  severe, 
and  in  spite  of  their  slow  speed  the  belts  do  not  have  a  long  life.  The 
quartz  ore  handled  there  breaks  with  very  sharp  fractures  and  is  apt  to 
cut  the  belt  by  impact  at  the  loading  point,  and  when  the  pickers  drag 
the  heavy  pieces  over  the  belt  and  over  its  edges.  In  some  plants  a  part 
of  the  conveyor  near  the  foot  is  set  on  an  incline  and  the  ore  is  washed  there 
by  water  sprays.  The  combination  of  hard,  sharp  ore  and  water  causes 
wear  on  both  sides  of  the  belt  and  on  pulleys  and  idlers  as  well. 


CHAPTER   XII 
LIFE   OF  BELTS 

Life  of  Belts. — The  life  of  a  belt  depends  upon  many  factors.  A  full 
discussion  of  them  would  be  a  review  of  what  has  already  been  said  about 
belts  and  their  accessory  parts.  We  may  put  down  in  a  list  a  number  of 
things  which  tend  to  shorten  the  life  of  a  belt,  see  page  197. 

The  belt  salesman  is  often  called  upon  to  answer  the  question,  "  How 
long  should  this  belt  last?"  With  some  knowledge  of  the  items  in  Table  32 
a  prudent  man  will  say  that  he  cannot  tell,  that  he  is  in  the  position 
of  an  actuary  of  a  life-insurance  company  when  asked  how  long  a  certain 
policy-holder  will  live.  It  is  possible  to  quote  tables  of  average  expectancy 
of  human  life;  it  is  also  possible  to  say,  from  a  knowledge  of  some  hundreds 
of  belt  conveyors,  that  in  handling  material  like  coal,  not  too  heavy  and 
not  too  abrasive,  a  rubber  belt  W  inches  wide  with  |-inch  cover  on  a  con- 
veyor 100-foot  centers  should  not  wear  out  before  it  has  carried  500 W2  tons, 
and  on  conveyor  200-foot  centers,  twice  as  much,  etc. 

This  rule,  if  it  may  be  called  a  rule,  is  based  upon  considerable  knowledge 
and  experience  in  making  and  selling  rubber  belts,  but  it  is  not  based  upon  a 
sufficient  number  of  cases  nor  has  it  been  under  consideration  long  enough 
to  be  called  authoritative.  It  is  never  offered  as  a  guarantee  by  the  con- 
cerns that  quote  it,  nor  is  it  ever  mentioned  in  considering  belts  for  coke, 
ores  and  minerals.  Its  application  to  any  specific  case,  even  for  coal  con- 
veying, is  so  conditioned  and  so  hedged  about  with  contingencies  that  it  is 
really  not  safe  to  offer  it  as  an  answer  to  the  question  cited  above  or  bring 
it  into  the  discussion  of  a  particular  conveyor. 

The  following  table  (Table  33)  gives  cases  taken  from  actual  practice 
and  compares  the  actual  tonnage  handled  with  the  tonnage  given  by  the 
statement,  Tons  =  500  TF2  per  100-foot  centers. 

Typical  Injuries  to  Belts. — Companies  in  the  business  of  making  belts 
or  selling  belt  conveyors  are  accustomed  to  receive  complaints  about  the 
quality  of  belts  somewhat  in  this  style:  "  The  belt  we  bought  from  you  on 
January  1st  has  lasted  only  six  months  and  is  going  to  pieces.  Our  previous, 
belts  all  lasted  two  years;  we  think  you  should  furnish  a  new  belt  or  make 
some  allowance  on  the  price  of  the  one  we  bought,  etc.,  etc."  Where  it  is 
possible  to  investigate  such  complaints,  it  will  generally  be  found  that 
the  cause  is  one  of  the  twenty-eight  items  given  in  Table  32.  For 
some  of  these,  the  seller  of  the  belt  may  be  responsible,  but  more  often  he  is 
not. 

196 


FACTORS  WHICH  SHORTEN  THE  LIFE  OF  A  BELT  197 


TABLE  32 

1.  Buying  a  cheap  belt — poor  frade  of  rubber  or  light-weight  fabric. 

2.  Buying  an  old  belt — rubber  dried  out,  no  elasticity. 

3.  Injury  to  belt  by  carelessness  in  getting  it  into  place  on  the  conveyor 

— cover  or  edges  torn. 

4.  Splice  not  square  with  the  belt — belt  runs  crooked,  wears  edges. 

5.  Material  too  hot — burns  holes  in  the  belt,  chars  the  cotton. 

6.  Material  corrodes  cotton  or  softens  rubber — plies  come  apart. 

7.  Loading  chute  of  poor  design — material  wears  the  belt  surface. 

8.  Skirt-boards  too  long  or  badly  set — belt  cut. 

9.  Loading  belt  directly  over  idler — belt  cut. 

10.  Speed  too  fast  for  proper  pick-up  of  lumps — belt  cut  or  abraded. 

11.  Speed  so  fast  that  belt  carries  only  thin  load — belt  wears  out  in 

center. 

12.  Cover  too  light  for  sharp  lump  material — belt  cut,  cover  worn. 

13.  Handling  wet,  sharp  material  through  a  tripper — cover  cut  and  worn. 

14.  Pulleys  too  small  at  drive,  take-up,  bend,  snub  or  tripper — plies 

come  apart. 

15.  Wide  gaps  between  idler  pulleys — belt  cracks  longitudinally. 

16.  Troughing  too  steep  for  thickness  of  belt — belt  cracks,  also  runs 

crooked. 

17.  Bad  alignment  of  conveyor — edges  rubbed  off,  or  worn  against  side- 

guide  idlers. 

18.  Too  many  side-guide  idlers — wear  off  edges  of  belt. 

19.  Too  many  fixed  trippers — belt  injured  by  reverse  bending  and  by 

putting  material  back  on  belt. 

20.  Excessive  take-up  tension — belt  stretches  and  splices  pull  out. 

21.  Reverse  bends  in  belt — plies  come  apart,  wear  on  pulley  rims  and  belt 

surface. 

22.  Exposure  to  snow,  rain,  sunlight — rubber  decays. 

23.  Lubrication  neglected — belts  cut  and  torn  by  worn  idlers. 

24.  Frequent  starting  under  full  load — belt  stretches  and  splices  pull  out. 

Slip  injures  belt  surface. 

25.  Discharge  chute  choking — material  catches  on  belt  and  tears  it. 

26.  Idler  pulleys  broken — belt  tears. 

27.  Lumps  falling  on  return  belt — jam   under  foot  pulley  and  tear   the 

belt. 

28.  Oil  or  grease  dropping  on  belt — rubber  softens  and  becomes  loose. 


198 


LIFE  OF  BELTS 


8 


« 


s  g 

o   fl 


3^  ^ 

PQAA 


§1 


leil 


»f  £  «T  tn     .  to"' 


« 
>>£>>>. 


1-1  04  CO  (N  (N 


CO  O  O  O  O  O  O  O  OC  O  ^f  C^l 


i-H_  rj<  !>•_  CO_  !>_  t^  CO_  »O  Tt*  I-H  O  O  —i  l^  CT>  ^ 


S«^   g   g   g   g^^   g   g 


2^1"^     .    »    .    .  o  o       " 

^  5  g'i'i'i'i  ^  **^ 

§  82  g  8  lijfi 


g  S^'oooo 


lOtOOCO'O'OOO'OO      'O 
C^  Is*  C^  O5  O5  O  O  O  t^*  O      '  O 


06"  oo"  oo"  od  r-T 


xxxxxxxxxxxxxxxx 


TYPICAL  INJURIES  TO  BELTS  199 

The  following  actual  cases  in  which  complaint  was  made  about  the  belt 
may  be  of  interest : 

1.  A  belt  at  a  by-product  plant. lost  a  strip  of  its  cover;   the  complaint 
was  based  on  "  poor  quality  of  rubber."     Examination  showed  that  the 
direction  of  tear  was  with  the  travel  of  the  belt,  so  that  it  could  not  have 
been  done  by  anything  catching  on  the  moving  belt.     Further  investigation 
proved  that  the  belt  had  been  torn  while  it  was  being  put  on  the  idlers. 
On  the  resistance  of  rubber  to  tearing,  see  page  30. 

2.  A  belt  gave  only  180  days  of  service  instead  of  a  year  as  other  belts 
had  lasted.     It  had  been  cut  by  a  tool  or  something  sharp  falling  on  the  belt. 

3.  A  belt  in  a  cannery  ran  in  a  tin-lined  trough  with  plows  (see  p.  158) 
at  intervals  to  discharge  the  farmers'  raw  material  into  bins.     The  belt  was 
injured  by  rough  joints  in  the  tin  trough.     When  the  material  was  dumped 
on  the  belt  it  contained  nails,  stones  and  sharp  sticks  which  the  plows  forced 
into  the  belt. 

4.  A  belt  handling  raw  fruit  in  a  cannery.     On  account  of  bad  alignment, 
the  edges  were  worn  and  the  acid  juice  corroded  the  cotton  fibers. 

5.  A  belt  carrying  wet  sand.     Edges  rubbed  off,  water  got  in,  plies  came 
apart. 

6.  A  belt  carrying  crushed  ore.     Ends  not  cut  square  at  the  splice;  belt 
ran  crooked,  edges  rubbed  off,  plies  came  apart. 

7.  A  cement  company  ordered  a  belt  without  stating  that  it  was  for  hot 
material.     The  rubber  dried  out  and  plies  came  apart.     Belts  can  be  spe- 
cially built  to  handle  hot  products  in  cement  mills  (see  p.  23). 

8.  A  belt  was  used  with  a  tripper  to  discharge  wet  gravel  into  a  row  of 
bins.     The  tripper  had  no  brush;    the  lower  pulley  forced  sharp  particles 
into  the  belt  and  the  cover  did  not  last  long. 

9.  A  coke  belt  lasted  only  one-third  as  long  as  was  expected.     The  coke 
was  not  properly  quenched;  hot  pieces  burned  holes  in  the  belt. 

10.  A  belt  carrying  crushed  stone  was  reported  to  be  wearing  out  rapidly. 
Investigation  showed  that  it  had  been  put  on  upside  down  with  the  f-inch 
rubber  cover  in  contact  with  the  pulleys;    the  side  that  carried  the  stone 
had  only  the  usual  3^  inch  of  rubber  intended  for  the  pulley  side. 

11.  When  a  certain  case  of  excessive  wear  on  one  edge  of  a  belt  was 
investigated  it  was  found  that  the  gauge  of  a  tripper  track  was  too  great  for 
the  wheels,  the  tripper  pulled  out  of  square  with  the  belt  and  the  latter 
bore  hard  against  the  side-guide  rollers  in  the  tripper  frame. 

12.  To  handle  wet  coal  under  unfavorable  conditions  it  had  been  found 
economical  to  use  balata  belts.     One  of  these  lasted  only  a  few  weeks  and 
was  replaced  on  the  claim  that  it  was  defective.     It  was  discovered  later 
that  hydrochloric  acid  spilled  on  a  floor  above  the  conveyor  had  dripped 
down  on  the  belt. 

Comparison  of  Life  of  Belts. — The  true  measure  of  belt  service  is  what 
the  belt  will  do  per  dollar  of  investment  or,  in  other  words,  what  it  costs 
per  ton  of  material  carried,  or  per  year  or  month  of  service  rendered.  There 
is  no  standard  of  comparison  for  this  because  operating  conditions  in  any 


200  LIFE  OF  BELTS 

two  plants  are  never  exactly  alike;  what  may  be  belt  extravagance  in  one 
plant  may  be  justifiable  practice  in  another.  A  certain  36-inch  8-ply  rubber 
belt  in  a  Western  smelter  (see  Table  33)  carried  over  7  million  tons  of  ore 
in  thirty-eight  months  at  a  cost  of  less  than  .02  cent  per  ton — a  most  excel- 
lent record.  On  the  other  hand,  if  a  belt  used  in  the  throwing  device  shown 
in  Figs.  167  and  192  lasts  one  week  and  carries  30,000  tons  at  a  cost  of  .4 
cent  per  ton,  it  is  considered  excellent  service,  although  the  rate  per  ton  is 
very  much  higher. 

It  is  often  unfair  to  judge  the  quality  or  the  suitability  of  various  kinds 
of  belts,  rubber  of  different  makes,  stitched  canvas,  balata  or  solid-woven 
belts  by  a  comparison  of  the  life  of  one  or  two  specimens.  As  has  been 
stated,  many  belts  must  be  replaced  because  of  abuse  or  accident,  not  on 
account  of  wear  in  service.  This  fact  is  well  known  in  the  belt  business; 
some  concerns  will  sell  belts  on  a  guarantee  of  a  certain  life  or  tonnage 
"  barring  abuse  or  accident  "  with  a  fair  certainty  that  under  the  operating 
conditions  the  belts  will  not  have  a  chance  to  wear  out,  but  will  meet 
with  one  or  more  of  the  mishaps  listed  in  Table  32,  page  197.  No  belt, 
whatever  the  type  or  make,  is  proof  against  all  of  the  items  mentioned, 
and  most  of  the  mishaps  will,  if  they  occur,  shorten  the  life  of  any  belt. 

Life  of  Rubber  Belts  in  Service. — During  the  past  thirty  years  concerns 
in  the  business  of  making  and  selling  rubber  belts  have  collected  much 
valuable  information  about  their  life  in  handling  materials  of  various 
kinds  under  many  conditions.  For  reasons  given  above,  this  information 
cannot  always  be  presented  in  a  way  to  convince  a  prospective  buyer  that 
a  certain  kind  of  belt  is  the  one  best  suited  to  his  operating  conditions. 
All  that  can  be  done  is  to  say,  with  some  authority,  what  has  happened 
under  similar  conditions  elsewhere.  From  this  knowledge  and  some  con- 
sideration of  the  principles  given  it  is  generally  possible  to  make  a  fair 
guess  as  to  which  belt  will  give  the  best  service  in  the  particular  place,  per 
dollar  of  cost. 

Table  33  prepared  from  information  furnished  by  several  manu- 
facturers of  rubber  belts,  gives,  in  addition  to  the  comparison  mentioned 
on  page  196,  a  statement  of  the  life  and  cost  of  certain  belts  per  ton  of 
material  carried  in  plants  carefully  managed.  Some  of  the  costs  per  ton 
are  exceptionally  low;  not  one  of  them  is  high. 

Belts  protected  from  sun,  snow  and  rain  last  longer  than  those  that 
work  in  the  open.  At  a  large  coke  plant  in  the  Middle  West,  rubber  belts 
carrying  run-of-mine  coal  on  an  open  bridge  spanning  the  storage  pile 
average  three  years  of  service.  Similar  belts  in  the  same  system  which  are 
protected  by  enclosures  average  nearly  five  years. 

Stitched  Canvas  Belts  in  Service. — Manufacturers  of  stitched  canvas 
belts  have  furnished  the  following  information: 

Table  34  is  a  record  of  5  conveyor  belts  used  by  one  company  in  bulk 
cargo  boats  carrying  crushed  limestone  and  run-of-mine  soft  coal  between 
ports  on  the  Great  Lakes.  The  belt  formed  part  of  a  mechanical  system 
for  discharging  the  boat's  cargo. 


STITCHED  CANVAS  BELTS  IN  SERVICE 


201 


TABLE  34.  — COMPARATIVE  SERVICE  OF  BELTS  CARRYING  LUMP 
LIMESTONE  AND  R.  OF  M.  COAL.  BELT  48-INCH,  10-PLY,  175  FEET 
LONG 

(Imperial  Be&ing  Co.,  Chicago) 


Belt  Cost  per 

Ton 

Kind  of  Belt 

Tons  Carried 

Cost  of  Belt 

of  Material 

Carried 

Cent 

Rubber  

416,249 

SI  287 

.309 

Solid-woven  cotton 

449  082 

982 

219 

Stitched  canvas 

574  402 

1033 

180 

Stitched  canvas                   .         

895,731 

1066 

119 

Stitched  canvas    

1,227,480 

1350 

110 

At  a  sand  and  gravel  washery  plant  in  northern  Illinois  300  feet  of  30- 
inch  8-ply  stitched  canvas  belt  ran  four  seasons  of  eight  months  each  and 
handled  1,497,000  tons  of  sand  and  gravel — a  record  for  the  plant. 

At  another  plant  of  the  same  kind  400  feet  of  24-inch  8-ply  stitched 
canvas  belt  on  an  incline  lasted  six  seasons  of  eight  months  each  and  handled 
1,235,000  tons  of  sand  and  gravel.  The  long  life  of  this  belt  may  be  attrib- 
uted in  part  to  the  fact  that  it  was  not  troughed  but  ran  flat. 

A  stitched  canvas  .belt,  18-inch  6-ply,  254  feet  long,  saturated  with  a 
Class  2  compound  (see  p.  48),  lasted  one  year  in  an  Illinois  cement  plant 
and  carried  143,000  tons  of  hot  cement,  which  was  4,000  tons  more  than 
the  combined  tonnage  of  two  belts  previously  used.  The  canvas  belt  was 
replaced  by  another  kind  of  belt  under  a  guarantee  of  equal  service,  but 
the  makers  of  it  had  to  furnish  four  belts  during  the  year  to  make  good  the 
guarantee.  When  the  year  was  up,  the  cement  company  put  in  another 
canvas  belt. 

A  36-inch  6-ply  canvas  belt  on  an  inclined  conveyor,  430-foot  centers, 
rising  80  feet,  speed  450  feet  per  minute,  over  22 £°  troughing  idlers  with 
snub  drive  from  54-inch  head  pulley,  carried  1,400,000  tons  of  run-of-mine 
coal  at  a  cost  of  less  than  3-  cent  per  ton. 

A  36-inch  8-ply  canvas  belt  on  22°  incline,  270-foot  centers,  running 
over  20°  troughing  idlers,  54-inch  lagged  head  pulley,  carried  1,000,000 
tons  limestone  crushed  to  6  inches  and  less. 

A  24-inch  5-ply  canvas  belt,  horizontal,  carried  723,000  tons  wet  screened 
and  washed  coal  for  less  than  yV  cent  per  ton. 


CHAPTER   XIII 
WHEN   TO   USE   BELT   CONVEYORS 

General  Advantages  of  Belt  Conveyors. — The  range  of  uses  of  belt 
conveyors  is  very  wide;  they  carry  all  kinds  of  bulk  materials  from  clippings 
of  tissue  paper  to  ore  in  pieces  weighing  200  to  300  pounds.  Package  goods 
of  all  sorts  except  the  heaviest  bales  and  barrels  are  successfully  handled. 

For  many  of  these  uses,  the  belt  conveyor  is  the  cheapest  and  best 
machine;  for  some  it  is  the  only  machine.  In  some  cases  it  is  the  only 
machine  that  will  give  the  required  capacity.  Capacity  is  generally  a 
matter  of  speed;  in  a  belt  conveyor,  it  is  comparatively  easy  to  get  high 
capacity  by  using  a  speed  high  enough,  for,  so  far  as  the  driving  of  the  belt 
is  concerned,  the  possible  speeds  are  far  beyond  all  needs  for  conveying. 
Belts  used  in  the  transmission  of  power  often  travel  5000  feet  per  minute, 
but  few  belts  except  some  used  in  grain  conveying  travel  over  600  feet  per 
minute.  Chain  conveyors,  on  the  other  hand,  seldom  travel  over  250  feet 
per  minute;  at  higher  speeds,  the  shock  and  noise  caused  by  chain  links 
engaging  with  the  sprocket  wheels  becomes  objectionable  and  the  wear 
in  the  chain  joints  becomes  troublesome. 

The  machinery  of  a  belt  conveyor  is  usually  simple  in  character  and  light 
in  weight;  it  is  not  likely  to  break  down  without  warning  and  it  generally 
consumes  less  power  for  the  work  accomplished  than  any  other  form  of 
conveyor. 

The  characteristics  mentioned  above  have  been  responsible  for  the  great 
development  and  wide  use  of  belt  conveyors.  In  the  choice  of  a  conveyor 
to  do  a  certain  work  in  a  particular  place  they  should  be  carefully  con- 
sidered, but  at  the  same  time  some  collateral  disadvantages  should  not  be 
overlooked.  These  do  not  apply  to  belt  conveyors  in  general,  but  rather  to 
specific  uses  as  referred  to  below. 

When  to  Use  Belt  Conveyors. — Since  a  belt  conveyor  will  carry  material 
horizontally  or  up  an  incline,  or  even  do  both  in  one  machine,  it  will  be  of 
interest  to  discuss  the  merits  of  belt  conveyors  as  compared  with  those  of 
conveyors  of  other  types  and  with  combinations  of  elevators  and  conveyors. 

Boiler  Houses. — Distribution  of  coal  in  overhead  bins  can  be  accom- 
plished by  belt  conveyor  or  flight  conveyor.  If  the  bin  is  a  long  continuous 
one,  a  belt  with  a  traveling  tripper  will  fill  it,  but  if  the  bins  are  short, 
with  spaces  between,  or  separate  round  tanks,  a  flight  convevor  is  more 
convenient  for  the  discharge.  Separate  fixed  trippers  could  be  used,  but 
they  wear  out  the  belt  by  repeated  reverse  bending  and  by  throwing  material 

202 


/"    BOILER  HOUSES  203 

back  on  the  belt  when  coal  is  to  be  carried  past  one  or  more  of  them.  To 
move  a  traveling  tripper  oven  clearance  spaces  while  the  belt  is  empty 
and  set  it  over  various  bins  requires  care  and  attention  on  the  part  of  the 
attendant  and  may  cause  delays  in  the  operation  of  the  machine.  Traveling 
trippers  with  large  storage  chutes  to  carry  the  discharge  from  the  belt  past 
clearance  spaces  and  then  drop  it  into  the  separated  bins  have  been  designed 
and  patented,  but  are  not  in  commercial  use. 

If  the  capacity  required  is  less  than  50  tons  an  hour,  the  work  is  less 
than  what  a  14-inch  belt  will  do  at  a  moderate  speed.  Twelve-inch  belts 
are  practically  obsolete;  14-inch  belts  are  hard  to  load  with  coal  larger 
than  2-inch  size.  For  small  capacities  a  belt  conveyor  will  cost  more  per 
foot  run  and  will  be  burdened  with  the  expense  of  the  tripper.  Narrow 
belts  are  apt  to  run  crooked  on  standard  commercial  idlers  and  suffer 
damage  when  they  are  held  to  place  by  side-guide  idlers. 

If  the  capacity  is  100  tons  an  hour  or  more,  belts  20  inches  or  more  in 
width  can  be  used.  These  are  easier  to  load  with  crushed  coal  and  they 
run  straighter  than  narrow  belts.  Belt  conveyors  in  this  class,  as  a  rule, 
cost  less  than  good  flight  conveyors  and  they  consume  less  power. 

If  the  conveyor  is  shorter  than  75  or  100  feet  a  flight  conveyor  may  be 
better.  All  of  its  length  can  be  used  for  distribution;  but  in  a  belt  con- 
veyor, 15  or  20  feet  is  lost  between  the  loading  point  and  the  point  of  first 
discharge  to  prevent  the  tripper  from  lifting  the  belt  under  the  chute  (see 
p.  169).  A  short  belt  wears  out  faster  than  a  long  belt  (see  p.  153),  and 
since  the  terminals  of  a  short  conveyor  use  more  power  than  the  run  of  the 
belt,  a  belt  conveyor  in  this  class  may  not  show  any  measurable  saving  of 
power  as  compared  with  a  flight  conveyor. 

If  the  length  of  the  conveyor  is  more  than  200  feet,  a  belt  will  show  a 
noticeable  saving  of  power,  and  for  lengths  over  300  feet  the  expense  of  a 
belt  conveyor  is  likely  to  be  less  than  the  cost  of  a  double-strand  conveyor 
with  roller  chains.  A  flight  conveyor  on  a  single  chain  will,  however,  cost 
somewhat  less  than  the  belt,  but  it  will  not  handle  large  coal  so  well.  It 
will  require  about  twice  as  much  power  as  a  belt  conveyor. 

If  quietness  of  operation  is  essential,  use  a  belt.  It  must  be  said,  how- 
ever, that  modern  roller  flight  conveyors  and  double-strand  roller-chain 
conveyors  are  much  quieter  than  old-style  flight  conveyors. 

If  the  conveyor  is  close  up  under  the  roof  and  receives  from  an  elevator, 
a  flight  conveyor  may  fit  in  better.  It  requires  less  head  room  than  a  belt 
with  a  tripper;  the  loading  chute  can  be  shorter  and  can  load  the  conveyor 
from  the  side.  A  belt  should  not  be  loaded  from  a  side-delivery  chute;  to 
load  it  properly  requires  more  height  than  to  load  a  flight  conveyor. 

The  belt  is  the  costly  item  in  a  belt  conveyor  and  at  the  same  time  the 
most  vulnerable  part.  If  it  receives  good  care  it  will,  in  places  suited  to 
it,  render  service  at  a  lower  cost  per  ton  of  material  carried  than  can  be 
shown  by  any  ordinary  flight  conveyor.  But  the  belt  may  be  damaged  or 
ruined  by  a  number  of  causes  and  then  the  charges  for  repair  or  renewal 
may  be  excessive.  The  ordinary  causes  of  belt  failure  are  given  in  Table  32. 


204  WHEN  TO  USE  BELT  CONVEYORS 

A  corresponding  list  of  causes  of  failure  of  flight  conveyors  would  be 
shorter.  In  general,  a  flight  conveyor  will  stand  more  abuse  and  will  work 
under  bad  conditions  and  under  a  lack  of  care  that  would  be  harmful  to 
belts. 

Transfer  of  Material  without  Distribution  by  Tripper. — In  this  case  the 
belt  makes  a  better  showing  than  a  flight  conveyor  except  for  short  dis- 
tances and  low  capacities.  For  feeders,  a  corrugated  steel  apron  costs  less 
than  a  wide  belt  with  the  right  number  of  plies  and  the  right  thickness  of 
cover.  It  is  less  likely  to  be  injured  by  tools,  sticks  and  hard,  sharp  lumps. 

The  belt  will,  however,  make  a  cleaner  delivery  of  material  at  the  head 
end  and  will  not  spill  so  much  on  the  return  run. 

On  inclines,  a  flight  conveyor  will  work  at  angles  steeper  than  25°,  but 
a  belt  will  not.  For  heavy  tonnages  a  steep  flight  conveyor  becomes  costly 
and,  as  between  the  two,  it  may  be  better  to  use  a  longer  belt  at  a  flatter 
angle,  or  even  two  belts  in  series  to  raise  the  material  to  the  required  height. 
Transfer  of  coal  at  by-product  plants  is  now  done  chiefly  by  belt.  Here  the 
distances  are  great  and  the  capacities  high.  Flight  conveyors  would  cost 
more  to  build  and  be  more  costly  to  drive.  The  disadvantages  of  belt 
conveyors  in  this  work  are  the  high  first  cost  of  the  enclosing  structures 
and  the  maintenance  of  them,  and  the  fact  that  the  bunkers  and  the  loading 
points  are  spread  apart  over  a  stretch  of  ground  which  would  otherwise 
be  unnecessary.  It  is  possible  that  such  plants  may  be  built  more  com- 
pactly in  the  future  using  large  skip  hoists  or  bucket  elevators  instead  of 
belt-conveyors. 

Crushed  Ores,  Gritty  Materials. — Belts  are  in  general  use  for  this  work. 

Lump  Rock,  Sand,  Gravel,  Excavated  Earth. — Belts  do  this  work  better 
than  any  metal  conveyors,  except  that  for  very  large  rock,  wide  apron 
conveyors  with  wood  or  steel  slats  will  stand  abuse  that  would  ruin  belts. 
They  cannot,  however,  be  economically  made  as  long  as  belt  conveyors. 

Ashes. — Many  belts  tried  on  this  work  have  failed  from  damage  by  hot 
cinders.  Moreover,  if  the  ashes  are  handled  wet,  the  cinders  cut  the  cover 
and  the  water  ruins  the  duck. 

Coke. — Belts  are  in  general  use.  The  grit  wears  out  metal  conveyors 
too  fast  for  economy.  Coke  is  too  friable  to  handle  in  scraper  conveyors. 

Wood  Chips. — Belts  are  in  general  use.  The  work  is  light  and  does  not 
require  expensive  belts. 

Package  Handling — Belts  are  in  general  use  for  all  except  the  largest 
packages  and  the  roughest  work. 

Zigzag  Conveyors  for  Elevating  Material. — In  a  few  places  a  rising 
series  of  short  inclined  belts  have  been  used  to  do  th'e  work  for  which  a 
bucket  elevator  or  a  skip  hoist  would  ordinarily  be  installed.  They  do  not 
save  in  first  cost;  they  take  up  more  space  and  require  more  power  than  a 
single  elevator.  Some  have  been  satisfactory  to  owners;  in  others  the 
short  belts  wore  out  rapidly  from  slip  due  to  the  steep  incline  (see  p.  142) 
and  from  abrasion  at  the  loading  point. 

In  the  matter  of  spare  parts  to  be  kept  on  hand,  there  is  this  difference, 


COMPARISONS  205 

Repair  parts  for  a  flight  conveyor  can  be  kept  on  hand  indefinitely,  but  a 
spare  rubber  belt  should  not  be  ordered  too  long  before  it  is  really  needed, 
or  it  will  deteriorate  in  storage  (see  p.  44).  Canvas  belts  suffer  less  in 
this  respect. 

Comparisons. — Where  comparisons  have  been  made  between  belt  con- 
veyors and  chain  conveyors  on  the  basis  of  tonnage,  length  or  cost,  the 
limits  are  not  hard  and  fast  and  between  them  there  are  chances  to  exercise 
some  personal  preference.  Both  kinds  of  machines  have  been  on  the 
market  for  many  years  and  have  been  to  a  great  extent  standardized. 
There  is  no  "  universal  conveyor  ";  for  handling  heavy  or  gritty  ores  as 
in  the  Western  smelters  or  in  conveying  heavy  tonnages  of  coal  over  long 
distances,  a  flight  conveyor  is  not  generally  considered,  but  in  many  places, 
boiler  houses  especially,  it  makes  the  best  distributor  even  though  it  does 
take  more  power  to  run  it.  The  older  forms  of  flight  conveyor  were  noisy, 
but  modern  roller  flight  conveyors,  or  roller  chain  conveyors  are,  by  com- 
parison, nearly  noiseless;  they  are  strong  and  rugged,  easy  to  load,  easy 
to  discharge,  spill  less  dirt  outside,  and  they  will  work  under  bad  conditions 
where  a  belt  will  fail.  Some  engineers  have  a  prejudice  against  scraping 
coal  in  a  trough.  It  does  take  more  power,  but  it  does  not  hurt  the  coal, 
even  anthracite  coal ;  and  as  for  the  wear  on  the  trough  the  item  of  replace- 
ment is  not  an  important  one.  It  is  a  fact,  however,  that  in  plants  like 
breakers  in  the  anthracite  coal  region  and  tipples  in  bituminous  districts 
where  nearly  all  the  coal  of  the  country  is  prepared  for  market,  chain 
conveyors  are  used  far  more  than  belt  conveyors. 

The  right  choice  of  a  conveying  machine  depends  upon : 

1.  A  proper  knowledge  of  the  limits  within  which  each  kind  works  best. 
This  implies  some  acquaintance  with  the  disadvantages  of  each  type  of 
machine.     The  advantages  are  usually  stated  in  manufacturers'  catalogues, 
proposals  and  advertising,  but  the  disadvantages  are  generally  learned  by 
experience. 

2.  A  recognition  of  the  fact  that  a  machine  highly  successful  in  one 
place  may  be  a  failure  in  another  place,  even  at  the  same  kind  of  work. 

3.  Proper  consideration  of  the  auxiliaries  necessary  to  the  operation  of 
the  conveyor.     A  simple  conveying  medium  with  complicated  auxiliaries 
for  feeding  or  discharge  may  be  less  desirable  than  a  more  complex  conveying 
medium  with  simpler  auxiliaries.     In  a  belt  conveyor,  for  instance,  the  belt 
itself  is  simple  and  strong,  but  it  requires  the  right  kind  of  a  chute  to  load 
it  safely,  and  to  effect  a  discharge  at  intermediate  points,  a  tripper,  with  its 
many  parts,  may  be  necessary.     A  flight  conveyor  has  a  chain  made  up  of 
many  parts,  but  feeding  is  simple  and  discharge  is  merely  dropping  the 
material  through  a  hole  in  the  trough.     A  screw  conveyor  is  not  economical 
of  power,  but  for  low  cost,  simplicity  of  mounting,  compactness,  ease  of 
feed  and  discharge,  and  for  cleanliness  and  avoidance  of  dust,  it  is  in  many 
places  preferable  to  any  other  kind  of  conveyor. 

Long-distance  Conveying  by  Belts. — On  this  subject,  see  page  107. 


SECTION  II.-BELT  ELEVATORS 


CHAPTER  XIV 


GENERAL   DESCRIPTIONS 


The  Elements  of  a  Belt  Elevator. — A  belt  elevator  for  bulk  materials 
consists  of: 

1.  Buckets  to  contain  the  material. 

2.  A  belt  to  carry  the  buckets  and  transmit  the  pull. 

3.  Means  to  drive  the  belt. 

4.  Accessories  for  loading  the  buckets  or  picking  up  the  material,  for 
receiving  the  discharged  material,  for  maintaining  belt  tension  and  for 
enclosing  and  protecting  the  elevator. 

Kinds  of  Belt  Elevators. — Any  kind  of  belt  with  buckets  attached  can 

Angular  Buckets 
Set  Close  Together 


Head  Pulley 


Pulley 


FIG.  200.— Head  of  Centrifugal 
Discharge  Belt  Elevator. 


FIG.  201.— Head  of  Belt  Elevator  with 
Continuous  Buckets. 


be  run  around  an  upper  pulley  and  a  lower  pulley,  and  it  will  elevate  loose 
material.  If  the  belt  speed  is  high  enough  the  contents  of  the  buckets  will 
be  thrown  out  in  passing  over  the  upper  pulley  (head  pulley)  and  will  fall 
into  a  chute  set  to  clear  the  descending  buckets,  some  distance  below  the 
head  shaft.  This  is  a  Centrifugal  Discharge  Elevator  (Fig.  200) ;  it  may  be 

207 


208  GENERAL  DESCRIPTIONS 

vertical  or  it  may  stand  at  an  angle.  Vertical  elevators  depend  entirely  on 
the  action  of  centrifugal  force  to  get  the  material  into  the  discharge  chute 
and  must  be  run  at  speeds  relatively  high.  Inclined  elevators  with  buckets 
spaced  apart  or  set  close  together  may  have  the  discharge  chute  set  partly 
under  the  head  pulley,  and  since  they  do  not  depend  entirely  on  centrifugal 
force  to  put  the  material  into  the  chute,  the  speeds  may  be  relatively  lower. 

Nearly  all  centrifugal  discharge  elevators  have  spaced  buckets  with 
rounded  bottoms;  they  pick  up  their  load  from  a  boot,  a  pit  or  a  pile  of 
material  at  the  foot  pulley. 

If  the  buckets  are  triangular  in  cross-section  and  are  set  close  on  the 
belt  with  little  or  no  clearance  between  them,  the  machine  is  a  Continuous 
Bucket  Elevator  (Fig.  201).  It  can  be  used  at  high  speed  with  centrifugal 
discharge  as  in  some  grain  elevators,  but  this  use  is  not  common.  The 
chief  use  of  continuous  bucket  elevators  is  to  carry  difficult  materials  at 
slow  speed.  Discharge,  in  this  case,  is  aided  slightly  by  centrifugal  force, 
the  contents  of  each  bucket  pouring  out  over  the  inverted  bottom  of  the 
bucket  ahead  of  it.  and  into  the  head  chute.  The  elevator  may  be  vertical 
or  inclined;  to  permit  the  buckets  to  be  loaded  directly  from  a  chute,  most 
elevators  of  this  kind  are  inclined;  very  few  pick  up  their  load  under  the 
foot  wheel. 

Elevator  Buckets. — The  general  requirements  for  an  elevator  bucket  are 
as  follows* 

1.  Dimensions  large  enough  to  pick  up,  hold,  and  discharge  the  largest 
pieces  of  the  material  handled  by  the  elevator. 

2.  Cubic  contents  enough  to  give  the  required  elevator  capacity  in  pounds 
per  minute,  or  tons  per  hour  or  per  day,  considering  the  speed  of  the  belt, 
the  bucket  spacing,  the  regularity  or  irregularity  of  loading  and  the  prob- 
ably incomplete  filling  of  the  buckets. 

3.  Strength  and  stiffness  to  pick  up  its  load  without  crushing  or  dis- 
tortion. 

4.  Thickness  of  metal  sufficient  to  resist  wear  to  an  economical  degree. 

5.  Inside  of  bucket  so  shaped  that  material  will  not  stick  there  and  fail 
to  discharge. 

To  meet  these  requirements  and  to  handle  the  many  kinds  of  bulk  mate- 
rials, buckets  for  belt  elevators  are  made  in  several  styles: 

1.  Buckets  with  rounded  bottoms,  the  kind  generally  used  in  centrif- 
ugal discharge  elevators. 

2.  Buckets  with  angular  bottoms,  sometimes  used  in  high-speed  centrif- 
ugal discharge   elevators  for  grain,  but  more  often  employed  in  continuous 
bucket  elevators  for  coarse,  heavy  materials. 

With  respect  to  their  construction  and  the  material  of  which  they  are 
made,  elevator  buckets  may  be  classified  thus: 

1.  One-piece  or  three-piece  buckets  of  tin  plate  or  light-gauge  sheet  steel, 
with  seamed  corners  and  reinforced  by  steel  bands.     These  are  used  for 
flour-mill  products  and  for  grain. 

2.  One-piece  buckets  of  heavier  steel,  pressed  to  form  and  riveted  or 


ELEVATOR  BELTS  209 

welded,   without    reinforcing  bands.     Used   for   grain   and   for   materials 
heavier  than  grain.  ^ 

3.  Hot-pressed  or  cold-pressed^  seamless  sheet-steel  buckets,  used  for 
grain  and  other  bulk  materials  not  too  heavy. 

4.  Cast   malleable-iron    buckets,   for    coal,   ores,   minerals   and   other 
coarse,  heavy  materials. 

5.  Two-piece  or  three-piece  buckets  of  heavy  steel  plate  made  with 
angular  bottoms  for  continuous  bucket  elevators. 

Elevator  buckets  are  described  more  fully  in  Chapter  XVI. 
Elevator  Belts. — The  general  requirements  for  an  elevator  belt  are : 

1.  Sufficient    flexibility    to    wrap   easily   around   the   head   and    foot 
pulleys. 

2.  Width  enough  to  fasten  the  elevator  buckets  securely  and  to  avoid 
twisting  or  turning  over  on  the  ascent. 

3.  Thickness  sufficient  to  transmit  the  working  pull  without  excessive 
stretch,  to  back  up  the  buckets  without  deflection  and  to  resist  the  tendency 
of  the  bucket  bolts  to  pull  through  the  belt. 

4.  A  protective  cover  or  a  body  of  fabric  thick  enough  and  strong  enough 
to  resist,  to  an  economical  degree,  the  surface  wear  in  elevators  that  handle 
sharp,  abrasive  materials. 

Practically  all  elevator  belts  in  this  country  are  made  of  cotton  fiber  in 
some  form;  they  are: 

1.  Rubber  belts. 

2.  Stitched  canvas  belts. 

3.  Balata  belts. 

4.  Solid-woven  belts. 

These  are  described  briefly  in  Chapter  I  and  more  fully  in  Chapters  III 
and  XVIII.  Leather  makes  a  good  elevator  belt  for  dry  work;  it  was  in 
general  use  for  that  purpose  up  to  fifty  years  ago,  but  now  fabric  belts  are 
cheaper,  more  economical,  and  better  suited  to  most  cases.  Elevators  with 
woven-mesh  steel-wire  belts  (Fig.  62)  have  been  used  in  Europe  for  light 
service,  but  they  are  unknown  in  this  country.  Elevators  with  buckets 
fastened  to  two  or  more  parallel  strands  of  wire  rope  have  been  tried  at 
various  times  but  without  success. 

Driving  the  Belt. — The  elevator  belt  is  driven  by  the  frictional  contact 
between  it  and  the  rim  of  the  head  pulley,  and  since  it  is  not  possible  to 
use  a  binder  pulley  or  snub  pulley  against  the  bucket  side  of  the  belt,  the 
angle  of  contact  is  limited  to  about  180°.  The  ability  of  the  head  pulley 
to  drive  the  belt  depends  (see  p.  109)  on  the  angle  of  belt  wrap  and  the 
coefficient  of  friction  between  the  belt  and  the  pulley  rim;  in  an  elevator 
both  of  these  are  fixed  within  certain  limits,  and  it  is  not  so  easy  to  increase 
the  driving  effect  as  in  a  belt  conveyor  (see  p.  110)  where  the  angle  of  wrap 
can  be  made  larger  than  180°.  To  get  more  pull  in  an  elevator  it  is  neces- 
sary to  put  tension  on  the  belt,  relatively  more  than  in  conveyors,  and 
this  leads  to  the  use  of  higher  unit  stresses  in  elevator  belts  than  in  conveyor 
belts. 


210  GENERAL  DESCRIPTIONS 

Belt  elevators  have  been  driven  at  the  foot,  but  the  drive  is  always  uncer- 
tain and  often  troublesome  (see  p.  283). 

Accessories  for  Loading  the  Buckets. — In  some  forms  of  elevating  and 
conveying  apparatus  it  is  possible  to  deposit  separate  charges  or  loads  in 
consecutive  buckets  as  they  pass,  by  means  of  a  mechanical  loader,  but 
at  the  speeds  at  which  centrifugal  discharge  elevators  run  that  cannot  be 
done;  the  material  cannot  be  guided  into  a  bucket  moving  at  a  rate  of  3  to 
10  feet  per  .second,  and  the  impact  would  scatter  and  spill  it.  At  the  lower 
speeds  of  continuous  bucket  elevators,  80  to  200  feet  per  minute,  the  diffi- 
culties of  mechanical  loading  are  less,  but  still  serious  enough  to  make  this 
process  expensive  and  troublesome.  It  is  much  easier  to  load  continuous 
buckets  by  means  of  a  chute,  especially  when  the  elevator  is  inclined,  so 
that  what  one  bucket  misses,  the  next  one  will  catch.  In  centrifugal  dis- 
charge elevators,  however,  it  is  never  possible  to  load  buckets  from  a  chute 
without  spill,  and  it  is  not  often  attempted;  it  is  necessary  in  all  cases 
to  let  the  buckets  pick  up  some  or  all  of  their  load  as  they  pass  around 
the  foot  wheel  or  as  they  enter  the  vertical  run.  If  the  elevator  digs  from  a 
pit  or  a  pile,  the  material  is  naturally  confined  to  the  path  through  which 
the  buckets  sweep,  but  otherwise  a  box  or  boot  is  used  to  form  a  mounting 
for  the  foot  shaft  and  keep  the  material  within  reach  of  the  buckets. 

Belt  Tension. — In  most  cases  the  foot-shaft  bearings  are  adjustable  in 
position  either  as  take-up  bearings  separate  from  the  boot  or  as  sliding 
bearings  which  form  part  of  the  boot.  Sometimes  the  foot-shaft  bearings 
are  fixed,  then  the  take-up  bearings  are  placed  at  the  head  of  the  elevator. 

Discharge  at  the  Head. — In  some  forms  of  chain  elevators  the  buckets 
discharge  on  the  lift,  but  all  belt  elevators  discharge  at  the  head  into  a 
chute  set  to  catch  the  material,  either  as  it  is  thrown  out  by  a  centrifugal 
discharge  elevator  (Fig.  200)  or  as  poured  out  by  a  continuous  bucket  ele- 
vator (Fig.  201).  The  position  of  the  chute  and  the  discharge  of  material 
from  the  buckets  depend  upon  three  factors: 

1.  The  speed  of  the  belt. 

2.  The  diameter  of  the  head  pulley. 

3.  The  spacing  and  shape  of  the  buckets. 

At  the  same  time,  the  loading  or  pick-up  at  the  foot  depends  upon: 

1.  The  speed  of  the  belt. 

2.  The  diameter  of  the  foot  pulley. 

3.  The  spacing  and  shape  of  the  buckets. 

The  best  speeds  for  the  pick-up  and  discharge  of  different  materials 
have  been  determined  by  trial  and  experiment,  and  have  been  confirmed 
by  years  of  successful  practice.  They  agree  so  well  with  results  given  by 
analysis  that  it  will  be  of  interest  to  show  how  they  can  be  established 
by  some  consideration  of  the  theory  of  the  subject.  This  discussion  will 
at  the  same  time  serve  as  an  introduction  to  the  further  consideration  of 
the  design  and  construction  of  belt  elevators. 


CHAPTER  XV 
CENTRIFUGAL  DISCHARGE   ELEVATORS 


Pick-up  and  Discharge  of  Elevator  Buckets. — When  a  mass  of  material 
of  weight  W  is  passing  around  a  wheel  it  is  under  the  influence  of  two  forces: 
one,  gravity,  acts  vertically  downward  with  a  force  W',  the  other,  centrif- 
ugal force,  acts  radially  outward  from  the  center  of  rotation  with  a  force  = 

Wvz 

,  where  v=  velocity  of  the  mass  in  feet  per  second,  g=  acceleration  of 

gR 

gravity  =32.2  feet  per  second,  and  R  is  the  radius  in  feet  to  the  center  of 
rotation. 

The  action  of  buckets  passing  under  a  foot  wheel  or  over  a  head  wheel 
is  shown  in  Fig.  202.  In  the  position 
3,  centrifugal  force  acts  horizontally 
outward,  gravity  acts  downward,  and 
the  diagonal  resultant  obtained  by 
completing  the  parallelogram  of  forces 
shows  by  its  direction  that  the  resultant 
pressure  is  downward  within  the  bucket, 
and  by  its  length  on  the  scale  to  which 
the  other  forces  are  drawn,  that  the 
pressure  is  \/2  =  1.414  times  the  weight 
of  the  mass  in  the  bucket  if  centrifugal 
force  and  weight  are  equal  in  amount. 
At  4,  the  pressure  decreases;  at  5  it 
becomes  zero  if  the  two  forces  are 
equal;  and  at  6  it  acts  to  propel  the 
mass  from  the  bucket  toward  a  chute 
set  to  catch  the  material  and  with  a 
force  which  on  the  scale  of  the  drawing 
equals  about  three-fourths  of  the  force 
of  gravity. 

Best  Speed  for  Elevator  Discharge. — In  order  to  deliver  material  to  the 
chute  without  spilling  or  scattering,  it  would  seem  that  at  a  place  near 
the  top  of  the  wheel  the  two  forces,  weight  and  centrifugal  force,  should 
be  equal  in  amount,  because  then,  for  the  position  5,  the  mass  within  the 
bucket  will  be  in  equilibrium  or  a  state  of  suspension,  neither  tending  to 
fly  out  upward  nor  to  fall  out  on  the  wheel,  but  ready  to  move  out  freely 
when  the  resultant  of  the  two  forces  on  the  descending  side  of  the  wheel 

211 


FIG.  202. — Action  of  Forces  on  Pick-up 
and  Discharge.  Centrifugal  Discharge 
Elevators  at  Speeds  Given  in  Table  35. 


212 


CENTRIFUGAL  DISCHARGE  ELEVATORS 


urges  the  material  toward  the  mouth  of  the  bucket.     That  condition  of 
equilibrium  exists  when 


Wv* 
W  =  --  (see  above)     or     v2  =gR. 


gR 


(1) 


or  since 


_2irRN 
~~ 


where  N  =  number  of  revolutions  per  minute,  then 

1 


54. 19 


VR 


(2) 


This  relation  between  radius  of  the  head  wheel  and  its  revolutions  per 
minute  holds  good  in  practice  for  the  discharge  of  liquids  or  dry  free-flowing 
materials  like  grain  from  elevator  buckets  of  ordinary  shape. 

Table  35,  calculated  from  equation  (2),  shows  diameters  of  head  wheels 
and  corresponding  speeds  for  the  entire  range  of  sizes  used  in  centrifugal 
discharge  elevators.  In  the  calculations,  assumptions  have  been  made 
for  the  thickness  of  belt  and  the  projection  of  buckets  ordinarily  used  with 
each  size  of  head  wheel,  and  R  has  been  taken  as  the  distance  from  the 
center  of  the  headshaft  to  the  center  of  gravity  of  an  average  load  in  the 
bucket. 

TABLE    35.— HEAD    WHEELS    AND    SPEEDS,    CENTRIFUGAL    DISCHARGE 

AT  HIGH  SPEED 


Diameter 

Revolutions 

Belt  Speed 

Diameter 

Revolutions 

Belt  Speed, 

of  Wheel, 

per 

Feet  per 

of  Wheel, 

per 

Feet  per 

Inches 

Minute 

Minute 

Inches 

Minute 

Minute 

12 

69 

217 

42 

39 

429 

15 

62 

247 

48 

37 

465 

18 

56 

264 

54 

35 

495 

21 

53 

292 

60 

33 

518 

24 

50 

314 

66 

32 

553 

27 

47 

333 

72 

31 

584 

30 

45 

353 

84 

29 

637 

33 

43 

372 

96 

27 

679 

36 

41 

386 

108 

25 

707 

39 

40 

408 

120 

24 

754 

In  this  discussion,  a  centrifugal  discharge  elevator  is  one  that  runs  at  a 
speed  high  enough  to  discharge  the  contents  of  the  buckets  clear  of  a  vertical 
run  of  descending  buckets. 

The  parabolas  drawn  from  positions  6  and  7  (Fig.  202)  represent  the 
path  of  discharge  from  buckets  in  those  positions.  The  material  all  clears 
the  head  wheel  and  will  enter  a  chute  with  its  upper  end  placed  to  clear  the 
descending  buckets  and  about  10°  of  arc  below  the  center  of  the  wheel. 


EFFECT  OF  HIGHER  SPEEDS 


213 


The  figure  shows  successive  positions  of  one  bucket,  not  simultaneous  posi- 
tions of  adjacent  buckets.  ^   " 

The  upper  half  of  Fig.  202  represents  the  action  on  a  head  wheel  and  the 
lower  half  shows  what  happens  on  the  bottom  of  a  foot  wheel.  If  the 
material  were  fed  in  on  the  descending  side  of  the  foot  wheel,  a  bucket  at 
position  10  could  not  retain  it  because  the  resultant  is  directed  toward  the 
mouth  of  the  bucket.  At  position  0  the  resultant  falls  within  the  bucket, 
but  nearly  all  the  material  would  flow  out  because  its  surface  would  tend 
to  lie  at  right  angles  to  the  line  of  pressure,  just  as  in  a  vessel  of  water 
whirled  around  an  axis,  the  water  surface  tends  to  stand  at  right  angles  to 
the  line  of  pressure  exerted  along  the  radius  of  rotation.  At  1  the  tendency 
to  squeeze  material  out  of  the  bucket  is  less  than  at  0,  and  at  2  it  is  still  less; 
but  even  there  it  would  be  impossible  for  a  bucket  to  retain  a  full  load 
under  the  influence  of  a  pressure  which  is  1.4  times  the  force  of  gravity  and 
is  directed  at  such  an  angle  that  when  the  material  d*'d  shift  to  square  itself 
with  the  line  of  pressure  some  of  it  would  fly  out  over  the  front  lip  of  the 
bucket. 

These  considerations  show  that  it  is  impossible  for  buckets  to  carry  free- 
flowing  material  like  grain  around  or  from  under  a  foot  wheel  when  the 
speed  of  travel  is  that  given  in  Table  35.  But  if  the  boot  is  so  arranged 
that  the  material  is  fed  in  above  the  level  of  the  foot  shaft,  as  in  Fig.  207, 
then  the  bucket  is  loaded  on  a  straight  lift  above  position  2,  where  centrif- 
ugal force  no  longer  acts  on  it.  When  a  boot  is  fed  at  the  back,  the  material 
is  swept  around  by  the  buckets,  but  the  buckets  fill  at  the  front  (see  Fig.  209). 

Effect  of  Higher  Speeds. — Fig.  203  shows  the  effect  of  making  centrif- 
ugal force  equal  to  twice  the  force  of  gravity,  a  condition  which  exists  when 
for  a  wheel  of  given  size  the  revolutions  per  minute  =1.414  =  \/2  times 
the  values  given  in  Table  35.  Con- 
sidering first  the  upper  half  of  the 
diagram,  as  representing  the  top  of  the 
head  wheel,  we  see  that  the  contents 
of  a  bucket  rising  to  the  position  3 
will  be  acted  upon  by  a  force  which 
is  \/5=2.23  times  as  great  as  the 
force  of  gravity.  The  direction  of 
the  force  shows  that  some  of  the 
material  must  be  suddenly  spilled 
over  the  front  lip  of  the  bucket.  Once 
over  the  lip,  the  spill  will  fly  outward 
and  fall  down  the  rising  leg  of  the 
elevator.  The  resultant  pressure  de- 
creases at  4,  but  at  5  the  direction  of 
the  pressure  is  vertically  upward  and 
some  of. the  contents  of  the  bucket  would  be  thrown  in  that  direction.  If 
the  scale  of  the  drawing  represents  a  96-inch  wheel  making  38  revolutions, 
the  spill  would  rise  about  3  feet  and  then  fall  down.  Any  material  remain- 


FIG.  203. — Action  of  Forces  on  Pick-up 
and  Discharge.  Centrifugal  Discharge 
Elevators  at  Speeds  41  Per  Cent  Higher 
than  Table  35. 


214 


CENTRIFUGAL  DISCHARGE  ELEVATORS 


ing  in  the  buckets  at  6,  7,  8  and  9  would  pass  off  in  the  parabolic  curves 
shown  in  the  figure. 

It  is  evident  that  with  the  spill  beginning  at  3  and  continuing  past  6 
there  would  be  a  whirling  shower  of  material  all  around  the  wheel  and  that 
only  a  part  of  what  the  buckets  picked  up  at  the  foot  would  reach  a  chute 
placed  in  any  position  near  the  head  wheel. 

Since  the  direction  of  the  resultant  of  pressure  shows  the  direction  in 
which  the  material  starts  to  leave  the  bucket  and  since  for  positions  5,  6,  7 
and  8  (Fig.  203)  these  lines  do  not  point  directly  toward  the  mouth  of  the 
bucket,  there  is  a  possibility  that  some  of  the  material  will  be  trapped 
within  the  bucket  and  descend  with  it,  or  at  least  require  the  chute  to  be  set 
low  to  catch  the  tail  end  of  the  scattering  discharge. 


Centrifugal 
Force 


FIG.  204. — Pressures  Affecting  Pick-up 
in  a  Grain  Elevator  with  Small  Foot 
Pulley. 


FIG.  205. — Pick-up  and  Discharge  at  Speeds 
30  Per  Cent  Lower  than  Table  35. 


When  the  lower  half  of  Fig.  203  is  compared  with  the  lower  part  of  Fig. 
202  it  appears  that  the  pressures  which  would  force  material  out  of  the 
buckets  under  the  foot  wheel  are  greater  in  amount  and  even  less  favorable 
in  direction  at  the  higher  speeds.  The  lower  half  of  Fig.  203  would  represent 
the  action  of  forces  in  an  elevator  boot  where  the  foot  pulley  is  half  as 
large  as  the  head  wheel,  but  if  the  pulley  is  only  one-third  or  one-fourth  as 
large  as  is  usual  in  large  grain  elevators  the  centrifugal  forces  are  then  three 

or  four  times  as  great  at  the  foot  as  at  the  head  since  the  force  varies  as  - 

R 

for  a  constant  value  of  v  (belt  speed).  Such  conditions  are  even  more 
unfavorable  for  filling  the  buckets  unless  the  loading  is  done  after  the 
buckets  are  on  the  straight  vertical  lift,  as  in  Fig.  207. 

Fig.  204  shows,  on  a  smaller  scale,  a  grain  elevator  with  a  96-inch  head 


EFFECT  OF  LOWER  SPEEDS  215 

wheel  and  a. 24-inch  foot  wheel.  The  resultant  pressures  (shown  to  proper 
scale)  which  prevent  the  grain  fr6m  entering  the  buckets  while  they  are  in 
contact  with  the  foot  wheel  are  6  ofc  7  times  as  great  as  those  which  throw 
the  grain  out  of  the  buckets  on  the  head  wheel.  It  is  quite  evident  that  the 
buckets  can  take  no  load  below  the  level  of  the  foot  shaft,  but  must  be  filled 
after  they  are  on  the  vertical  run. 

Effect  of  Lower  Speeds. — Fig.  205  shows  the  effect  on  pick-up  and 
discharge  when  the  speed  is  lower  than  the  best  speed  in  the  ratio 

1  to  —j=.  =  1  to  .7,  a  condition  which  makes  centrifugal  force  one-half  the 

force  of  gravity  and  N  about  seven-tenths  the  values  given  in  Table  35. 
Considering  the  upper  half  as  representing  the  top  of  the  head  wheel,  a 
loaded  bucket  rising  to  the  position  3  will  not  spill  any  of  its  load  because 
the  resultant  pressure  differs  very  little  from  W  (due  to  the  force  of  gravity) 
either  in  amount  or  in  direction.  The  same  condition  exists  at  4,  but  at  5 

W 
there  is  a  downward  force  equal  to  —  which  would  tend  to  spill  some  material 

out  of  the  bucket  onto  the  top  of  the  wheel.  At  6  the  resultant  shows  that 
more  would  spill  out  and  at  7  the  remaining  material  would  be  thrown  clear 
of  the  wheel  and  could  be  caught  in  a  chute,  the  upper  end  of  which  is 
set  to  clear  the  descending  buckets  and  on  about  45°  of  arc  below  the 
center  of  the  wheel. 

Such  a  discharge  can  be  used  for  an  inclined  elevator,  but  it  is  too  slow 
for  a  vertical  elevator. 

For  a  discussion  of  the  discharge  from  inclined  elevators,  and  of  the 
point  at  which  discharge  begins  see  Chapter  XXII  and  Fig.  285. 

Belt  Speeds  for  Different  Materials. — From  what  has  been  said  it  is 
evident  that  the  figures  of  Table  35  apply  to  free-flowing  materials 
which  can  be  piled  deep  in  a  boot  and  to  buckets  which  finish  their  loading 
while  on  the  vertical  run  above  the  center  of  the  foot  wheel. 

It  does  not  apply  to  substances  like  coal,  ores,  minerals,  cinders,  etc., 
which  are  not  free-flowing,  or  which  contain  lumps,  or  which  are  apt  to  be 
wet  and  stick  to  the  buckets.  It  is  not  safe  to  pile  such  materials  deep 
in  a  boot;  the  work  of  pulling  buckets  through  the  mass  would  be  wasteful 
of  power,  and  buckets  would  be  broken  or  torn  loose  by  the  severe  strain. 
When  the  materials  of  that  kind  are  handled  in  a  centrifugal  discharge  ele- 
vator with  spaced  buckets,  the  feed  must  be  tangent  to  the  sweep  of  the 
buckets  and  not  so  high  up  that  the  foot  wheel  would  be  dangerously  buried 
in  case  the  amount  of  feed  should  exceed  the  lifting  capacity  of  the  buckets 
for  a  short  time.  It  is  customary  to  use  sloped  front  boots  (Fig.  259) 
for  such  work  and  the  travel  of  the  buckets  while  on  the  foot  wheel  must 
be  limited  to  a  speed  at  which  centrifugal  force  will  not  throw  material 
out  of  the  bucket  at  positions  1  and  2  (Fig.  202).  This  tendency  to  throw 
material  out  is  resisted  at  position  1  by  the  pressure  between  the  moving 
bucket  and  the  material  flowing  into  the  boot  or  lying  on  the  bottom  of 
the  boot;  and  at  position  2  by  the  fact  that  coarse  substances  like  coal, 


216 


CENTRIFUGAL  DISCHARGE  ELEVATORS 


minerals,  etc.,  are  not  so  free-flowing  as  to  be  squeezed  out  of  the  bucket 

by  a  resultant  pressure  of  the  direction  and 
intensity  shown  in  Fig.  202. 

Nevertheless,  it  is  not  practicable  to 
use  the  speeds  of  Table  35  for  coal,  ores, 
minerals,  cinders  and  similar  coarse  ma- 
terials, and  there  are  other  reasons  why 
that  table  should  not  be  used  for  dusty 
materials.  For  these  various  materials, 
and  even  for  free-flowing  materials  under 
certain  conditions  it  is  proper  to  use  the 
speeds  of  Table  36  which  are  82  per  cent 
of  those  of  Table  35.  At  these  speeds 
centrifugal  force  is  two-thirds  the  force  of 
gravity  and  the  conditions  of  discharge 
are  shown  in  the  upper  part  of  Fig.  206. 
Reasons  for  Table  36. — Some  important 

FIG.  206.— Pick-up  and  Discharge     reasons  are   given  in    a  paragraph  above; 

to  these  may  be  added  the  following: 

1.    Foot    wheels     for    various    reasons 
are  often  made  smaller  than  head  wheels. 

Centrifugal    force    is    then    greater    than    at    the    head,    since    for    the 

same  belt  speed  or  velocity  v,  centrifugal  force  varies  as  —  (see  p.  211); 

R 

that  is,  it  is  twice  as  great  for  a  wheel  half  as  large.  That  difference,  in  the 
greatest  degree  existing  in  practice,  is  shown  in  Fig.  204,  but  even  where  the 
belt  speed  is  less  and  the  difference  between  the  foot  wheel  and  the  head 
wheel  is  not  so  great,  the  action  at  the  foot  may  be  such  as  to  prevent 
buckets  from  loading  properly.  Fig.  206  shows  to  scale  what  happens  in 
an  elevator  for  coal,  etc.,  where  the  speed  is  according  to  Table  36 
and  the  foot  wheel  half  as  large  as  the  head,  say,  18  and  36  inches,  respec- 
tively. The  pressures  due  to  centrifugal  force  which  hinder  the  filling  of 

TABLE    36.— HEAD    WHEELS    AND    SPEEDS,    CENTRIFUGAL    DISCHARGE 
AT  MODERATE  SPEED 


at  Speeds  given  in  Table  36. 
Foot  Wheel  Half  as  Large  as 
Head  Wheel. 


Diameter 

Revolutions 

Belt  Speed 

Diameter 

Revolutions 

Belt  Speed, 

of  Wheel, 

per 

Feet  per 

of  Wheel, 

per 

Feet  per 

Inches 

Minute 

Minute 

Inches 

Minute 

Minute 

12 

56 

176 

39 

33 

337 

15 

51 

200 

42 

32 

352 

18 

46 

217 

48 

30 

377 

21 

43 

237 

54 

28 

396 

24 

41 

257 

60 

27 

424 

27 

39 

276 

66 

26 

449 

30 

37 

290 

72 

25 

471 

33 

36 

311 

84 

23 

506 

36 

34 

320 

96 

22 

554 

ELEVATORS  FOR  DIFFERENT  KINDS  OF  MATERIAL 


217 


the  buckets  while  they  are  on  the  18-inch  foot  wheel  are  more  than  three 
times  as  great  as  those  which  throw  the  material  out  of  the  buckets  while 
they  are  on  the  36-inch  head  wheel.  If  the  foot  wheel  were  24  inches  in 
diameter  (ratio  f ),  the  pressures  as  to  intensity  and  direction  would  be  the 
same  as  those  shown  in  Fig.  202;  if  the  wheel  were  27  inches  (ratio  f)  they 
would  be  more  favorable  for  the  filling  of  the  buckets;  if  the  wheels  were  of 
the  same  size,  i.e.,  36  inches,  the  opposing  pressures  would  be  still  less, 
the  buckets  would  take  their  load  lower  down  in  the  boot,  with  less  turmoil 
and  stir  in  the  material,  and  they  would  carry,  in  most  cases,  a  fuller  load. 

2.  If  the  materials  are  picked  up  and  discharged  at  high  speed,  the  wear 
on  buckets  is  serious;   there  is  the  risk  of  damaging  them  or  tearing  them 
loose,  the  strain  in  the  elevator  belt  or  chain  is  apt  to  be  injurious,  the  wear 
on  the  head  chute  may  be  objectionable,  and  with  some  friable  materials, 
like  coal,  the  breakage  from  striking  the  chute  violently  may  be  a  dis- 
advantage. 

3.  Overcoming  the  friction  losses  at  high  speeds  means  a  waste  of  power. 


FIG.  207. 


FIG.  208. 


FIG.  209. 


FIG.  207. — Pick-up  in  High-speed  Grain  Elevator,  with  Front  Feed  at  Level  of  Foot  Shaft. 
FIG.  208. — Front  Feed  below  Level  of  Foot  Shaft. 
FIG.  209.— Back  Feed. 

Practical  considerations  like  these  have  established  the  following  rules: 

High  Speed  Grain  Elevators. — If  the  material  is  dry,  granular,  free- 
flowing,  not  abrasive,  not  damaged  by  picking  up  or  throwing  down  at 
high  speeds,  and  if  high  capacity  is  desired,  use  Table  35. 

This  is  preeminently  the  table  for  high-speed,  high-capacity  grain 
elevators. 

Boots  for  high-speed  grain  elevators  should  have  the  front  feed  inlet 
so  high  and  the  front  of  the  boot  and  the  lower  part  of  the  casing  so  shaped 
that  the  buckets  can  complete  their  loading  after  passing  above  the  center 
of  the  foot  wheel  in  its  upper  position.  Fig.  207  shows  how  grain  is  picked 
up  in  such  a  boot;  if  the  feed  in  front  is  low,  as  in  Fig.  208,  the  pick-up 
is  not  improved,  the  buckets  may  not  take  a  full  load,  some  of  the  grain 
may  lie  comparatively  dead  in  the  feed  hopper,  or  the  chute  may  be  choked. 
If  the  feed  is  at  the  back  (Fig.  209)  there  is  no  gain  in  placing  the  chute 
high,  but  if  it  is  tangent  to  the  sweep  of  the  buckets  in  the  upper  position 
of  the  foot  wheel,  then  if  the  elevator  is  choked  to  a  standstill  before  the 


218  CENTRIFUGAL  DISCHARGE  ELEVATORS 

feed  is  stopped,  less  grain  will  flow  into  the  boot  and  less  will  have  to  be 
shoveled  out  to  clear  the  boot  in  starting  up  again. 

Discharge  chutes  for  high-speed  grain  elevators  may  be  set  so  that  the 
lip  just  clears  the  buckets  and  lies  on  an  arc  15°  or  20°  below  the  center 
of  the  head  wheel.  On  this  point,  see  page  303. 

Limitations  of  High  Speed. — So  far  as  discharge  is  concerned,  Table  35 
applies  to  all  kinds  of  centrifugal  discharge  grain  elevators,  but  there  are 
certain  practical  limitations  to  its  use:  when  the  feed  chute  is  high  and 
the  buckets  finish  their  loading  above  the  level  of  the  boot  wheel  there 
is  danger  of  burying  the  wheel  if  the  feed  should  be  too  heavy,  or  if  the 
driving  motor  should  stop  by  failure  of  electric  current,  or  if  the  elevator 
should  slow  down  or  stop  for  any  other  reason.  This  is  particularly  true 
when  the  wheel  is  all  the  way  down  in  the  lowest  position  of  take-up  travel. 
High-speed  grain  elevators  with  foot  wheels  one-fourth  as  large  as  the 
head  wheels  are  more  liable  to  choke  than  those  with  foot  wheels  relatively 
larger,  or  where  the  speed  is  more  moderate.  Hence,  unless  the  elevator 
belt  is  relatively  wide  in  proportion  to  the  projection  of  the  buckets,  so 
that  it  has  plenty  of  pulley  contact  at  the  head,  and  unless  plenty  of  power 
is  provided  to  pull  the  buckets  through  an  accidental  accumulation  of 
material  in  the  boot,  it  is  better  to  use  a  moderate  speed,  like  those  given 
in  Table  36,  and  make  the  foot  wheel  at  least  half  as  large  as  the  head  wheel. 

A  moderate-speed  grain  elevator  with  a  foot  wheel  half  as  large  as  the 
head  wheel  can  use  any  of  the  standard  makes  of  boot  with  rounded  bottom 
and  in  which  the  bottom  of  the  feed  chute  enters  at  or  above  the  level  of  the 
foot  shaft  in  its  lowest  position.  If  the  foot  wheel  is  not  so  large  as  the 
ratio  £,  more  power  is  spent  in  stirring  up  the  grain  in  the  boot  and  unless 
the  feed  chute  is  set  relatively  higher  up,  the  buckets  will  not  fill  properly 
and  the  feed  chute  may  choke. 

Discharge  chutes  for  grain  elevators  at  the  speeds  of  Table  36 
should  be  set  about  30°  below  the  center  of  the  head  shaft. 

If  the  material  is  fine,  dry  and  dusty  the  speed  should  be  kept  low  to 
give  the  buckets  time  to  free  themselves  of  air  in  passing  through  the 
material  in  the  boot;  otherwise  they  do  not  fill  properly  but  stir  up  the 
material  uselessly  and  raise  an  objectionable  dust.  Besides  that,  the  fan 
action  of  the  pulley  and  buckets  at  the  head  may  disturb  the  air  enough  to 
blow  the  material  out  of  the  chute  or  waste  it  down  the  elevator  legs. 

For  flour,  bran,  chaff  and  similar  mill  products  of  light  weight  use 
Table  36  up  to  24-inch  head  wheels,  but  not  beyond.  The  foot  wheel  should 
be  as  large  as  the  head  wheel  if  possible,  certainly  not  less  than  three-fourths 
of  that  size.  The  feed  should  be  rather  high;  the  lip  of  the  discharge  chute 
should  be  20°  to  25°  below  the  center  of  the  head  wheel. 

For  fine  cement,  pulverized  lime  and  other  dry,  dusty  substances 
weighing  more  than  50  pounds  per  cubic  foot,  use  Table  36  up  to  42-inch 
head  wheels,  but  not  beyond.  The  ratio  of  head-wheel  to  foot-wheel  diam- 
eter should  not  be  over  4  to  3;  if  for  any  reason  the  diameter  of  the  foot  wheel 
is  limited  to  18  inches,  for  example,  the  head  wheel  must  be  in  proportion; 


ELEVATORS  FOR  VARIOUS  KINDS  OF  MATERIAL  219 

in  this  instance  it  should  not  be  larger  than  24  inches.  The  feed  should  be 
rather  high;  the  lip  of  the  discharge  chute  should  be  about  30°  below  the 
center  of  the  head  shaft. 

• 

If  the  material  is  hard,  gritty  and  lumpy,  like  coal,  ashes,  coke,  stone, 
ores,  salt,  fertilizers,  coarse  chemical's,  or  if  it  is  moist  at  times,  as  coal  is, 
and  apt  to  stick  to  the  buckets,  use  Table  "36.  The  speed  of  bucket 
travel  and  the  number  of  revolutions  of  the  head  shaft  are  determined  by  the 
allowable  wear  and  tear  on  the  buckets  and  on  the  belt  or  chain,  and  not 
especially  by  the  discharge  of  the  buckets  at  the  head.  Belt  elevators 
carrying  coal  crushed  to  1  \  inches  and  less  are  run  successfully  at  nearly  500 
feet  per  minute  on  72-inch  head  wheels;  but  400  feet  per  minute  (54-inch 
wheels)  may  be  considered  the  permissible  limit  for  belts  carrying  coal 
larger  than  2  inches  and  a  still  lower  speed,  say,  350  feet  per  minute  (42-inch 
wheels),  should  be  used  for  rougher,  harder  and  more  abrasive  materials 
to  keep  wear  and  tear  within  tolerable  limits.  Chain  elevators  are  never 
run  over  350  feet  per  minute,  and  on  very  coarse  materials  300  feet  is  a 
safer  limit.  If  the  lumps  are  larger  than  3  inches  it  is  better  not  to  use  a 
centrifugal  discharge  elevator,  but  rather  a  slow-speed  machine  of  some 
other  type. 

For  ease  in  pick-up,  and  to  fill  the  buckets  properly,  make  the  foot  wheel 
at  least  two-thirds  as  large  as  the  head  wheel.  If  the  space  at  the  foot  is 
limited,  and  must  be  made  no  larger  than,  say,  18  inches,  then  the  head  wheel 
should  not  be  larger  than  27  inches.  Fig.  206  shows  that  when  the  head 
wheel  is  twice  the  size  of  the  foot  wheel  the  pressures  which  hinder  the  filling 
of  the  buckets  are  more  than  three  times  the  forces  which  throw  materials 
out  of  the  buckets  at  the  head.  Fig.  202  shows  how  the  pick-up  is  improved 
when  both  wheels  are  of  the  same  size.  In  general,  the  larger  the  foot 
wheel,  the  easier  the  pick-up  and  the  better  the  filling  of  the  buckets. 
On  this  point  see  p.  214. 

If  for  a  certain  capacity  it  is  necessary  to  run  buckets  at,  say,  350  feet 
per  minute,  the  head  wheel  should  be  42  inches  in  diameter  (see  Table 
36)  and  the  foot  wheel  should  be  at  least  28  inches,  30  inches  would  be 
better,  36  inches  still  better.  If  there  is  room  for  only  a  20-inch  foot  wheel, 
for  instance,  there  are  several  things  which  may  be  done:  (1)  make  the 
head  wheel  20  inches  xf  =  30  inches,  run  the  belt  at  290  feet  per  minute 
(Table  36)  and  get  the  required  capacity  by  a  closer  spacing  of  buckets  or 
by  using  larger  buckets;  (2)  make  the  head  wheel  larger  than  30  inches 
and  the  belt  speed  more  than  290  feet,  and  have  an  elevator  wasteful  of 
power,  and  with  a  capacity  not  up  to  normal  because  of  buckets  running 
only  partly  full;  (3)  use  some  other  kind  of  elevator. 

The  boot  for  coal  and  similar  coarse  substances  may  be  of  any  shape 
that  will  deliver  the  material  to  the  sweep  of  the  buckets  if  the  following 
requirements  are  met :  (1)  it  must  not  choke  the  feed  inlet  with  dead  material 
when  the  foot  wheel  is  in  its  high  position  with  the  take-up  all  the  way  up; 
(2)  the  feed  must  not  be  so  high  that  it  can  easily  overflow  or  swamp  the 
foot  wheel  when  it  is  in  its  lowest  position.  For  these  reasons,  most  grain 


220 


CENTRIFUGAL  DISCHARGE  ELEVATORS 


boots  do  not  make  good  boots  for  coal,  etc.  The  boots  generally  sold  for 
this  service  are  made  with  sloped  fronts  (see  Figs.  259  and  261). 

The  discharge  chute  should  be  set  with  its  lip  at  least  30°  below  the 
center  of  the  head  shaft;  45°  is  better  for  coal  and  other  materials  which 
are  damp  at  times,  and  if  the  materials  wet  and  fine  it  is  well  to  place  the 
chute  even  lower  than  the  "45°  line. 

Table  37  refers  to  elevators  in  which  the  discharge  occurs  without 
the  assistance  of  centrifugal  force.  These  are  generally  slow-speed  inclined 
elevators,  for  which  see  Chapter  XXII. 

TABLE    37.— HEAD     WHEELS,     SPEEDS,     BUCKET     SPACING,     INCLINED 
ELEVATORS,   CENTRIFUGAL  DISCHARGE  AT  LOW  SPEED 


Diam- 
eter of 
Wheel, 
Inches 

Revo- 
lutions 
per 
Minute 

Belt 
Speed, 
Feet  per 

Minute 

Bucket 
Pro- 
jection, 
Inches 

Bucket 
Spacing, 
Inches 

Diam- 
eter of 
Wheel, 
Inches 

Revo- 
lutions 
per 

Minute 

Belt 

Speed, 
Feet  per 
Minute 

Bucket 
Pro- 
jection, 
Inches 

Bucket 
Spacing, 
Inches 

12 

35 

110 

3 

9.4 

27 

24 

175 

7 

21.2 

15 

31 

124 

8| 

11.8 

30 

23 

180 

8 

23.5 

18 

28 

132 

4 

14.1 

33 

22 

190 

9 

25.9 

21 

27 

147 

5 

16.5 

36 

21 

198 

10 

28.2 

24 

25 

157 

6 

18.8 

Elevators  for  liquids  can  be  run  at  the  speeds  of  Table  35  with  buckets 
of  the  shape  shown  in  Fig.  202.  In  order  to  be  filled  full,  the  buckets 
should  complete  their  loading  above  the  center  of  the  foot  shaft;  or  in  other 
words,  the  foot  shaft  must  be  submerged.  If  for  any  reason  the  foot  shaft 

must  be  kept  above  the  level  of  the  liquid  in 
the  tank,  or  boot,  it  is  important  to  make  the 
wheel  large,  first,  to  maintain  a  good  depth 
of  liquid  below  the  shaft  for  the  buckets  to 
act  on;  second,  to  avoid  the  high  pressures, 
almost  radial  in  direction  (see  Figs.  204  and 
206)  which  prevent  the  buckets  from  filling 
under  the  foot  wheel  when  the  latter  is  smaller 
than  the  head  wheel. 

If  the  elevator  has  buckets  of  ordinary 
shape  it  cannot  be  expected  to  carry  a 
volume  of  liquid  per  minute  or  per  hour  based 
upon  the  rated  liquid  capacity  of  the  bucket, 
as  stated  in  makers'  catalogues,  because  even 
if  the  foot  wheel  is  larger  than  the  head 
wheel,  the  directions  of  the  resultant  pressures 
under  the  foot  wheel  are  such  as  to  squeeze 
some  of  the  liquid  out  of  them.  Buckets  with 
a  high  front  like  Fig.  226  are  better  in  that 
respect.  Fig.  210  shows  the  pressures  in  an  elevator  run  at  a  speed  given 
in  Table  35  and  with  a  foot  wheel  twice  as  large  as  the  head  wheel. 


FIG.  210. — Pick-up  oi   Liquids  in 
Centrifugal  Discharge  Elevator. 


ELEVATORS  FOR  LIQUIDS  AND  PULPS  221 

Although  elevators  are  not  built  with  such  large  foot  wheels,  the  figure  is 
useful  in  showing  how  the  filling  can  be  improved  in  a  high-speed  elevator. 
Since  the  surface  of  the  liquid  in  tlje  bucket  tends  to  lie  at  right  angles  to 
the  line  of  resultant  pressure  (see  p.  213).  the  contents  of  a  bucket  at  position 
1  would  lie  parallel  to  A — A ;  and  at  2,  B — B  represents  the  surface,  at  that 
instant,  of  what  the  bucket  holds.  Of  course,  the  pressure  due  to  the 
depth  of  liquid  exerts  a  modifying  influence  at  position  1,  and  the  splash 
or  the  disturbed  level  of  liquid  in  the  boot  may  put  more  in  the  bucket  at 
position  2;  nevertheless  it  is  an  observed  fact  that  if  the  buckets  of  a 
centrifugal  discharge  elevator  are  expected  to  pick  up  liquid  below  the 
level  of  the  foot  shaft  they  lift  only  a  small  fraction  of  their  nominal  capacity. 

Pulps  handled  in  the  wet  concentration  of  ores,  and  other  similar  flowing 
mixtures  of  solids  and  liquids,  behave  like  liquids  as  far  as  pick-up  is  con- 
cerned; and  what  is  said  above  applies  to  them  also,  that  is,  for  a  good 
pick-up  the  foot  pulley  should  be  larger  than  the  head  pulley.  At  the  same 
time,  the  head  pulley  must  not  be  too  small.  Table  35  gives  proper  rela- 
tions of  belt  speed  and  diameter  of  head  pulley  for  high  speeds.  Table  36 
gives  similar  data  for  slower  speeds. 

If  the  percentage  of  solids  in  the  pulp  is  high,  and  if  the  solids  are  heavy 
and  tend  to  settle  in  the  bottom  of  the  bucket  on  the  lift,  the  contents  of  a 
bucket  are  not  discharged  in  a  single  mass,  but  the  bulk  of  the  water  leaves 
first  and  the  solids  are  later  in  leaving.  This  has  the  effect  of  delaying  the 
discharge,  and  hence  while  the  head  receiver  or  chute  for  liquids  like  water 
or  very  thin  pulps  may  be  set  quite  high  at  the  head  of  a  centrifugal  dis- 
charge elevator,  say,  15°  or  25°  below  the  center  of  the  head  shaft,  the  lip 
of  the  receiver  should  be  considerably  lower  for  heavy  pulps  in  which  the 
percentage  of  solid  is  high.  For  these  45°  is  often  not  enough;  10°  or  15° 
additional  may  be  necessary  in  some  cases. 

If  the  receiver  is  set  low  for  the  reason  mentioned  above,  it  is  better  to 
run  the  elevator  at  a  speed  given  in  Table  36;  the  pick-up  at  the  lower 
speed  will  be  somewhat  improved  and  the  buckets  will  have  a  chance  to 
take  a  larger  load. 

Delayed  Discharge. — The  theory  of  elevator  discharge  discussed  in  the 
preceding  paragraphs  assumes  that  the  material  leaves  the  bucket  with  no 
frictional  resistance.  It  is  possible  to  assume  a  coefficient  of  friction  between 
the  material  of  which  the  bucket  is  made  and  the  contents  of  the  bucket, 
and  from  a  known  velocity  and  radius  of  rotation,  calculate  how  far  beyond 
the  vertical  a  bucket  will  be  before  the  tangential  force  overcomes  the  fric- 
tional resistance  within  the  bucket.  Such  calculations  lead  to  no  practical 
result.  The  coefficient  of  friction  is  an  uncertain  quantity  and  in  comparison 
with  roughnesses  and  dents  in  the  buckets  and  the  resistance  offered  by 
one  or  two  rows  of  nuts  and  washers  across  the  discharge  opening  its  effect 
is  small. 

All  that  can  be  said  with  certainty  is  that,  owing  to  the  items  mentioned, 
some  of  the  material  is  delayed  in  discharge  and  some  may  be  spilled. 
When  the  head  chute  of  an  elevator  is  set  according  to  the  rules  given  above 


222  CENTRIFUGAL  DISCHARGE  ELEVATORS 

it  will  catch  practically  all  of  the  material,  including  that  which  is  delayed 
in  discharge.  In  any  elevator  there  is  always  some  scatter  or  spill  which 
will  not  reach  the  chute,  but  that  amount  should  be  small  and  it  cannot  be 
avoided. 

Rules  for  Speeds  of  Centrifugal  Discharge  Elevators  sometimes  state 
the  travel  of  the  chain  or  belt  in  feet  per  minute  without  reference  to  the 
size  of  the  head  wheel.  Such  rules  are  worthless.  For  proper  discharge, 
each  size  of  head  wheel  has  its  own  best  speed.  Those  given  in  Table  35 
and  Table  36  represent,  respectively,  the  best  speeds  for  free-flowing 
materials  and  also  for  those  which  are  heavy,  coarse  and  not  free-flowing. 
The  figures  for  the  number  of  revolutions  per  minute  are  whole  numbers 
which  differ  from  results  of  equation  (2),  page  212,  by  less  than  unity. 
Where  it  is  not  convenient  to  get  these  exact  speeds  by  the  use  of  standard 
sizes  of  pulleys,  gears,  sheaves,  etc.,  used  in  the  transmission  of  power  to 
the  elevator  head,  a  revolution  more  or  less  will  make  no  noticeable  differ- 
ence in  the  pick-up  or  in  the  discharge. 

For  emphasis  it  may  be  worthwhile  to  repeat  the  statement  that  the 
success  of  a  centrifugal  discharge  elevator  may  depend  on  the  size  of  the  foot 
wheel  and  the  way  material  is  fed  to  the  buckets.  If  the  foot  wheel  is 
smaller  than  the  head  wheel  it  may  revolve  so  fast  that  the  buckets  pick 
up  no  material  at  all  while  they  are  passing  around  the  wheel,  especially 
if  the  material  is  fine  and  free-flowing.  With  such  materials  the  feed  should 
not  be  too  low.  When  elevators  are  equipped  with  low-feed  boots  and 
small  foot  wheels,  they  may  work,  but  at  a  reduced  capacity.  Sometimes 
they  are  absolute  failures. 

The  fact  that  grain  buckets  do  not  take  their  load  below  or  behind  the 
foot  pulleys  is  quite  evident  when  a  boot  like  that  shown  in  Fig.  271,  page 
295,  is  fed  at  the  back,  where  the  buckets  are  going  down.  At  such  times, 
unless  the  front  opening  is  closed,  not  only  will  dust  come  out,  but  the  grain 
itself  will  be  thrown  clear  out  of  the  boot.  This  is  especially  true  when,  as 
in  many  grain  elevators,  the  bottom  of  the  front  opening  is  lower  than  the 
upper  position  of  the  foot  shaft.  5V  r  the  best  feed  from  the  front,  the 
opening  should  be  about  as  shown  in  Fig.  271. 

Evidence  from  Photographs. — The  speeds  and  revolutions  of  head 
wheels  given  in  Tables  35  and  36  are  confirmed  by  successful  practice 
and  have  been  verified  by  instantaneous  photographs  of  the  discharge 
from  the  buckets.  Some  of  these  are  given  in  Figs.  211,  212,  213,  214, 
which  show  the  action  of  8  by  5  inch  buckets  spaced  12  inches  apart  and 
running  over  36-inch  head  wheels  at  various  speeds.  In  Fig.  211  the  wheel 
makes  35  r.p.m.  and  the  buckets  make  a  clean  discharge  of  pebbles  weigh- 
ing 80  pounds  per  cubic  foot.  In  Fig.  212  there  is  a  clean  discharge  of 
oats  at  the  same  speed,  although  oats  weigh  only  30  pounds  per  cubic  foot. 
In  Fig.  213  the  wheel  makes  20  revolutions  or  180  feet  per  minute  chain 
speed,  but  the  pebbles  from  bucket  A  are  beginning  to  spill  out  on  the 
chain  while  the  discharge  from  B  hits  the  inverted  bottom  of  C.  Fig.  214 
shows  a  bad  discharge  of  oats  at  23  r.p.m.  =210  feet  per  minute. 


EVIDENCE  FROM  PHOTOGRAPHS 


223 


FIG.  211. 


FIG.  212. 


FIG.  213. 


Fia.  214. 


FIGS.  211-214. — Instantaneous  Photographs  of  Centrifugal  Discharge  at  Various  Speeds 

of  36-inch  Head  Wheel. 


224  CENTRIFUGAL  DISCHARGE  ELEVATORS 

Point  where  Discharge  Begins. — In  the  calculations  for  Table  35  it  is 
assumed  that  centrifugal  force  equals  the  force  of  gravity,  or  vz  =  gR  (Equa- 
tion 1,  p.  212)  and  then  discharge  begins  at  the  top  of  the  wheel;  but  the 
lower  values  of  Table  36  are  based  on  centrifugal  force  =f  the  force  of 
gravity,  or  v2  =  %gR,  so  that  the  values  of  v  in  Table  36  are  V^66  =  .82  of 
those  in  Table  35.  For  this  condition  discharge  will  begin  later  and  at 
angle  from  the  vertical  whose  cosine  is  f  (see  p.  312).  This  angle  is  about 
48°.  The  correctness  of  this  reasoning  is  shown  by  Fig.  211,  where  the 
contents  of  bucket  A,  about  45°  from  the  vertical,  are  just  beginning  to 
come  out,  the  mass  of  pebbles  at  C  being  entirely  clear  of  bucket  B.  Simi- 
larly in  Fig.  212,  the  oats  from  B,  which  is  65°  from  the  vertical,  are  almost 
clear,  the  mass  at  D  having  been  discharged  from  bucket  C. 

Sizes  of  Head  Pulleys  for  Centrifugal  Discharge  Elevators. — From 
what  has  gone  before  it  is  evident  that  there  are  three  factors  which  deter- 
mine the  size  of  head  pulleys.  (1)  That  relation  between  diameter  and 
revolutions  per  minute  which  gives  a  clean  discharge  according  to  Tables 
35,  36  and  37  and  which  gives  a  belt  speed  sufficient  for  the  quantity  of 
material  to  be  handled.  (2)  the  necessity  of  having  the  diameter  of  the 
pulley  at  least  five  inches  for  each  ply  of  the  belt  as  discussed  in  Chapter  V 
and  Chapter  XX.  (3)  In  cases  where  the  size  of  the  foot  wheel  is  limited,  a 
ratio  between  diameters  of  head  pulley  and  foot  pulley  which  will  permit  the 
buckets  to  fill  properly,  see  pages  218  and  219. 


CHAPTER  XVI 


ELEVATOR  BUCKETS 


Discharge  as  Related  to  Shape  of  Buckets. — In  Fig.  202,  representing  the 
conditions  of  discharge  in  high-speed  elevators,  the  direction  of  the  resultant 
for  position  7  shows  that  if  the  bucket  were  made  with  the  front  parallel 
with  the  back  there  would  be  interference  between  the  front  and  some  of  the 
grain  leaving  the  bucket,  and  that  the  discharge  would  be  delayed  or  some 
grain  would  be  trapped  within  the  bucket.  In  Fig.  203,  representing  the 
discharge  at  abnormally  high  speed,  the  resultants  at  5,  6,  7,  8  and  9  are 
all  directed  toward  the  lip  of  the  bucket;  in  Fig.  205,  showing  the  discharge 
at  abnormally  low  speeds,  the  resultants  all  point  toward  the  back  of  the 
bucket,  and  in  Fig.  206,  which  represents  the  conditions  established  by 
Table  36,  the  resultant  is  parallel  with  the  back  of  the  bucket  and  there  is 
no  tendency  to  trap  the  material. 

These  considerations  show  that  at  the  higher  speeds  a  clean  discharge  is 
favored  by  having  the  top  angle  T  of  a  bucket  relatively 
small  (Fig.  215)  and  the  bottom  angle  B  relatively  large, 
so  that  the  bucket  presents  a  wide-open  mouth  for  the 
release  of  its  contents.  But  on  the  other  hand,  the 
bucket  lip  must  not  be  too  low,  nor  the  bottom  angle  too 
large,  or  some  of  the  material  will  be  spilled  from  the 
bucket  at  position  3  (Fig.  202).  The  shapes  of  .various 
styles  of  centrifugal  discharge  elevator  buckets  on  the 
market  represent  compromises  between  these  opposing 
factors.  Of  all  the  buckets  for  elevating  grain,  the  Buffalo 
bucket  (Fig.  216)  is  most  generally  used  for  high  speeds; 
it  has  a  top  angle  of  80°  and  a  bottom  angle  of  20°. 
Empire  buckets  have  a  top  angle  83°  and  a  bottom  angle  15°;  they  are 
large  in  cross-section,  but  will  not  discharge  at  the  speeds  of  Table  35. 
Rialto  buckets  with  a  top  angle  of  70°  and  a  bottom  angle  of  30°  or  40° 


FIG.  215.— Typical 
Round  -  bottom 
Bucket  for  Cen- 
trifugal  Dis- 
charge. 


Bofialo     Favorite  4.  Empire      Rialto        Salem  &  Acme,        Style  A&AA 

Style  A 


yle  B 


Style  0 


FIG.  216. — Angles  of  Various  Sheet-steel  and  Malleable  Iron  Elevator  Buckets. 

225 


226  ELEVATOR  BUCKETS 

will  discharge  at  speeds  even  higher  than  those  of  Table  35,  but  for  the 
same  over-all  dimensions  they  hold  less  than  Buffalo  buckets.  The  Minne- 
apolis (Fig.  217)  bucket,  which  is  often  sometimes  run  at  very  high  speeds, 
is  in  cross-section  approximately  an  equilateral  triangle 
with  straight  sides  and  60°  angles.  It  will  give  a  clean 
discharge  at  speeds  higher  than  standard,  but  it  is  more 
apt  to  spill  when  the  rising  bucket  meets  the  head  wheel 
because  the  resultant  pressure  at  that  point  has  the 
direction  AB  at  standard  speeds.  For  still  higher  speeds 

the  resultant  AC  is  greater  in  amount   and   even  more 

ant  Pressures  in  unfavorable  in  direction  (see  "  Effect  of  High  Speeds," 
"Minneapolis"  p.  213)  and  acts  to  squeeze  still  more  grain  over  the 
Bucket^on^Meet-  front  Hp  Jt  ig  doubtful  whether  there  is  any  gain  in 

Pulley.  capacity  by  increasing  the  speed  of  these  buckets 

more  than  20  per  cent  over  the  figures  given  in  Table 
.35  At  still  higher  speeds  the  spill  increases  rapidly,  the  discharge  is 
scattering,  and  much  of  the  power  consumed  by  the  elevator  is  spent  in 
forcing  the  buckets  through  the  boot  at  excessive  speed  and  in  lifting  more 
grain  than  is  delivered  to  the  chute  at  the  head.  In  one  elevator  equipped 
with  these  buckets  the  head  pulley  is  72  inches,  makes  56  r.p.m.  with  a 
belt  speed  of  1055  feet  per  minute;  here  centrifugal  force  is  3.2  times 
gravity.  At  the  24-inch  foot  pulley  it  is  9.6  times  gravity.  If  a  diagram 
for  these  conditions  is  drawn  similar  to  Fig.  204  it  will  be  seen  that  the 
resultant  pressures  are  practically  radial,  the  buckets  fill  entirely  on  the 
vertical  run  and  begin  to  discharge  as  soon  as  they  meet  the  head  pulley. 

Malleable-iron  buckets  in  Style  A,  Fig.  216,  have  a  top  angle  65°  and  a 
bottom  angle  40°  and  are  well  suited  to  handle  nearly  all  rough  and  heavy 
materials  at  the  speeds  given  in  Table  36.  For  materials  that  are  wet  and 
stringy,  or  which  stick  to  the  bucket,  a  bucket,  like  Style  B,  Fig.  216,  with  a 
lower  front  will  give  a  cleaner  discharge.  For  material  like  raw  sugar,  which 
is  very  sticky,  the  wide-open  mouth  of  the  Style  C  bucket  (Fig.  216)  gives 
a  better  discharge  and  the  material  is  not  so  apt  to  pack  tight  in  the  bottom. 

The  discharge  at  the  head  of  a  centrifugal  discharge  elevator  is  affected 
also  by  the  shape  of  the  bottom  of  the  bucket;  since  this  point  is  related  to 
the  spacing  of  the  buckets  it  is  discussed  below. 

Discharge  as  Affected  by  Spacing  of  Buckets. — Fig.  213  shows  the  dis- 
charge from  bucket  B  striking  the  bottom  and  front  of  bucket  C,  which  is 
1  foot  ahead  of  it,  but  if  the  buckets  were  2  feet  apart  there  would  be  no 
such  interference,  because  in  Fig.  213  the  direction  of  the  discharge  from 
B  shows  that  the  mass  would  clear  bucket  D  2  feet  ahead  of  B  even  at  the 
low  speed  of  180  feet  per  minute.  At  higher  speeds  the  buckets  may  be 
closer  together,  and  as  may  be  seen  from  Fig.  212  the  spacing  for  the  condi- 
tions shown  might  be  even  less  than  1  foot  and  still  the  discharge  from  bucket 
B  would  clear  the  bucket  ahead  of  it. 

A  comparison  of  Figs.  202  and  203  shows  that  as  the  speed  increases, 
the  material  is  thrown  more  nearly  in  a  radial  direction  from  the  wheel  and 


DISCHARGE  AS  AFFECTED  BY  SPACING  OF  BUCKETS        227 

with  less  chance  of  interfering  with,  the  leading  bucket.  The  shape  of  the 
bucket  also  has  a  bearing  on  the  Spacing;  if  the  bottom  is  sharp  or  of  small 
radius  and  lies  close  to  the  belt,  th£  discharge  from  the  following  bucket  is 
not  so  likely  to  strike  it,  and  if  the  discharge  should  strike  it,  a  straight 
bottom  is  less  likely  to  scatter  the  discharge  than  a  full,  rounded  bottom. 
This  explains  why  buckets  of  the  Minneapolis  type  (Fig.  221)  can  be  placed 
close  together,  almost  touching,  on  a  belt  and  run  at  high  speeds;  the 
mouth  is  wide  open  to  permit  a  discharge  similar  to  that  shown  in  Fig.  203, 
and  if  the  discharge  from  one  bucket  does  hit  the  bottom  of  the  one  ahead, 
the  grain  is  not  scattered,  perhaps  hardly  deflected  from  its  path. 

Buckets  of  the  Buffalo  type  (Fig.  216)  have  a  bottom  sharper  and  less 
rounded  than  Empire  buckets  and  hence  can  be  placed  closer  together 
without  making  a  scattering  discharge.  Fig.  218  shows  to  scale  Buffalo 
buckets  8  inches  deep,  8  inches  projection,  spaced  13  inches  on  a  grain  ele- 
vator belt  passing  over  a  96-inch  head 
pulley  that  makes  27  revolutions  per  min- 
ute. This  speed  is  according  to  Table  35 
and  the  conditions  of  discharge  are  shown 
in  Fig.  202.  The  resultants  drawn  from 
positions  6  and  7  represent  the  direction 
of  the  arrows  shown  in  Fig.  218,  and  the 
buckets  13  inches  ahead  of  those  positions 
are  shown  dotted.  It  is  probable  that 
some  of  the  discharge  from  6  hits  the  FIG.  218. — Discharge  of  Grain  from 
sloping  bottom  of  the  bucket  13  inches  ahead  15  X8-inch  Buffalo  Buckets  Spaced 
and  glances  off,  but  the  discharge  is  most 

active  at  7,  where  the  resultant  pressure  is  greater,  and  so  directed  that  the 
grain  will  clear  the  bucket  13  inches  ahead  of  position  7.  The  13-inch 
spacing  gives  satisfactory  results  with  the  8  by  8-inch  Buffalo  buckets  in  the 
particular  elevator  which  Fig.  218  illustrates,  and  the  amount  of  spill  is 
very  small. 

Kinds  of  Elevator  Buckets.  Seamed  Buckets. — In  elevators  for  grain, 
flour-mill  products,  etc.,  where  the  abrasion  is  not  severe,  it  is  customary  to 
use  light  sheet-steel  buckets;  most  of  them  are  of  the  three-piece  style  with 
reinforcing  band.  The  body  sheet  of  tin  plate  or  light  sheet  steel  No.  24 
or  No.  26  gauge,  is  bent  to  form  and  fastened  by  lock  seams  to  the  two 
end  pieces.  The  reinforcing  band  around  the  top  edge,  about  1  or  l£  by 
|  inches  in  section,  forms  a  digging  edge  in  front  and  a  hold  for  the  bucket 
bolts  in  the  back  and  gives  the  bucket  the  necessary  stiffness  to  resist 
distortion  without  excessive  weight.  In  high  elevators  run  at  high  speed 
it  is  important  to  avoid  unnecessary  weight  in  the  buckets;  a  heavy  bucket 
costs  more,  adds  to  the  loacl  on  the  belt,  and  under  the  influence  of  the 
centrifugal  forces  existing  in  high-speed  elevators  it  is  more  likely  to  be 
torn  loose  from  the  belt  or  pull  the  bolts  through  the  belt. 

Seamed  buckets  are  sold  by  a  number  of  manufacturers  under  trade- 
names  which  are  well  known  in  this  country. 


228 


ELEVATOR  BUCKETS 


The  Buffalo  bucket  (Fig.  219)  is  made  in  sizes  from  12  to  20  inches  long, 
with  a  brace  for  added  stiffness  in  the  sizes  over  15  inches.  The  back  is 
usually  curved  so  as  to  match,  to  some  extent,  the  bend  of  the  belt  as  it 

wraps  around  the  pulley.  This 
has  some  advantage  in  reducing 
the  pull  on  the  bucket  bolts  in 
picking  up  the  load  (see  Fig.  243), 
but  at  the  same  time  it  concen- 
trates the  pressure  between  the 
back  of  the  bucket  and  the  belt 
on  two  spots,  and  belts  are  some- 
times cut  through  at  those  places. 
When  the  buckets  are  made  with 
a  flat  back,  the  wear  on  the  belt 
is  more  distributed. 

Rialto  buckets  (Fig.  220)  are 
made  in  sizes  up  to  20  inches 
long;  they  will  discharge  clean 
at  high  speed,  and  because  of 
their  shallow  form  and  relatively 

large  bottom  angle  (see  p.  225)  they  can  be  placed  closer  together  on  a  belt 
than  Buffalo  buckets. 

Buckets  of  the  styles  known  as  Empire,  Favorite,  etc.  (Fig.  216),  are 
made  in  a  great  variety  of  sizes  from  5  to  20  inches  long.  They  have  bottoms 
more  fully  rounded  than  other  styles  and  will  nominally  hold  more  for  the 
same  over-all  dimensions.  Because  of  their  depth  and  the  shape  of  their 


FIG.  219.— Buffalo  Buckets. 


FIG.  220.— Rialto  Bucket. 

bottoms  they  must  be  spaced  relatively  further  apart  to  avoid  interference 
in  discharge,  and  hence  the  net  carrying  capacity  is  not  greater,  even  under 
conditions  favorable  for  fully  loading  the  buckets.  They  are  not  often  used 
in  high-speed  elevators  (Table  35),  but  rather  in  elevators  of  moderate 
capacity  where  the  speed  is  within  the  limits  of  Table  36.  They  are, 
therefore,  well  suited  to  handle  flour,  bran,  chaff  and  other  fine,  dry,  light 
materials,  as  well  as  grain. 

"  Minneapolis  "  buckets  are  made  in  all  sizes  up  to  20  inches.  Fig. 
221  shows  the  usual  construction,  sheet-steel  body  of  No.  18  or  No.  20 
gage  with  a  binding  strip  around  the  top. 


PRESSED  AND  RIVETED  BUCKETS  229 

Pressed  and  Riveted  Buckets — One  of  the  oldest  buckets  on  the  market 
is  the  Salem  bucket  (Fig.  222).  »It"is  a  one-piece  bucket  with  a  front  nearly 
straight,  rounded  bottom,  and  co#iers  riveted  together  or  spot-welded  on 
the  back.  In  the  lighter  gauges  a  reinforcing  strip  is  folded  over  the  top 
edge  of  the  back.  The  front  or  lip  is  not  usually  reinforced.  In  heavier, 
gauges  the  back  strip  is  not  used,  in  which  case  the  central  portion  of  the 
back  is,  as  it  were,  depressed  below  the  ends  of  the  back  by  the  thickness 


FIG.  221.— Minneapolis  Bucket.  FIG.  222.— Salem  Bucket. 

of  the  metal,  since  the  ends  are  bent  around  on  the  outside  of  the  back  and 
spot-welded  or  riveted  there.  This  compensates  to  some  degree  for  the 
crown  of  the  pulley  (see  p.  261)  when  these  buckets  are  fastened  to  a  belt. 
Salem  buckets  are  made  in  sizes  from  2  by  2  inches  to  24  by  8  inches  in 
various  thicknesses  of  metal,  No.  16  and  heavier,  and  as  to  shape,  either  the 
standard  high  front,  Style  A  (Figs.  222  and  223)  or  special  low  front,  Style  B 
like  Fig.  224.  These  low-front  buckets  discharge  more  readily  than  Style  A, 
but  they  hold  much  less  on  vertical  lifts.  There  is  not  so  much  difference 
in  inclined  elevators,  because  the  B  bucket  can  carry  a  high  surcharge 


FIG.  223.— Style  A  Acme  Bucket.  FIG.  224.— Style  B  Acme  Bucket. 

without  spilling  it  over  the  front  lip.  For  that  reason,  and  because  they 
discharge  readily  at  low  speeds,  they  are  often  used  in  inclined  elevators 
when  the  angle  of  inclination  from  the  vertical  is  30°  or  more. 

Acme  buckets  (Figs.  223  and  224)  are  like  Salem  buckets  in  shape, 
but  the  riveted  or  welded  lap  is  on  the  ends  instead  of  on  the  back.  They 
are  made  in  sizes  2£  by  2£  inches  to  20  by  8  inches,  Styles  A  and  B. 

In  the  lighter  gauges,  Salem  and  Acme  bucket  are  used  in  moderate- 
speed  elevators  for  grain  and  light  mill  products,  pulverized  chemicals  and 
similar  materials;  in  the  heavier  gauges  they  are  used  for  materials  heavier 
than  grain,  but  they  will  not  handle  coarse,  heavy  substances  so  well  as 
malleable-iron  buckets. 


230 


ELEVATOR  BUCKETS 


Seamless  sheet-steel  buckets,  known  also  as  Caldwell  or  Avery  buckets, 
are  made  of  one  piece  of  soft  sheet-steel  pressed  in  dies  similar  in  form  to 
Salem  buckets.  The  corners  are  rounded,  and  the  bucket  is  stiff  enough 
for  work  in  grain  and  similar  materials.  It  is,  however,  more  expensive 
than  most  three-piece  buckets  because  of  the  heavier  metal  used.  As 
compared  with  light  buckets  with  a  reinforced  top  edge,  seamless  buckets 
dig  their  load  more  easily  and  can  be  run  with  less  power. 

Comparative  Capacities. — Table  38  shows  that  the  carrying  capacities 
of  various  styles  of  grain  buckets  do  not  differ  much  when  expressed  as 
cubic  feet  per  foot  of  belt,  because  the  buckets  of  fuller  cross-section  must 
be  spaced  further  apart  to  get  a  clean  discharge. 

TABLE  38.— CARRYING  CAPACITY  OF  GRAIN  ELEVATOR  BUCKETS 

PER  FOOT  OF  BELT 


Style 

LengthX  ProjectionX  Depth 
Inches 

Contents  of 
One  Bucket, 
Cubic  Feet 

Spacing, 
Inches 

Cubic  Feet 
per  Foot 
of  Belt 

Salem  .  .        

20X7X7 

.33 

14 

28 

Buffalo  
Rialto  

20X7X7 
20X  7X  6^ 

.33 

.28 

13 
12 

.30 

28 

Empire  

20X  7X  7 

.36 

16 

27 

Minneapolis  ... 

20X7X7| 

.23 

8^ 

32 

FIG.  225. — Manufacturers'  Standard  Malleable  Iron  Buckets. 

Malleable -iron  Buckets. — Prior  to  1908  there  was  no  uniformity  or 
regularity  of  sizes  and  shapes  of  malleable-iron  buckets  as  made  by  different 
manufacturers.  In  that  year  the  present  Manufacturers'  Standard  Sizes 


MALLEABLE  IRON  BUCKETS 


231 


were  established;  the  older  styles  and  sizes  have  since  become  obsolete. 
The  standard  A,  A  A,  B  and  C»  buckets  shown  in  outline  in  Fig.  216  are 
illustrated  also  in  Fig.  225.  The^ottoms  are  rounded  to  a  rather  large 
radius  and  each  end  is  flared  outward  at  a  slope  of  6°;  since  there  are  no 
seams  or  rivets,  the  buckets  fill  and  discharge  readily  and  material  is  not 
apt  to  stick  in  them.  The  metal  is  thicker  than  in  most  sheet-steel  buckets, 
the  corners  are  filleted  and  thickened;  hence  malleable-iron  buckets  are 
stiffer  and  stronger  than  most  steel  buckets  of  corresponding  size  and  shape 
and  they  suffer  less  from  distortion  and  abrasion  in  service.  They  are  also 
less  affected  by  rust. 

Style  A. — Over  75  per  cent  of  the  malleable-iron  buckets  sold  in  this 
country  are  Manufacturers'  Standard  Style  A ;  they  are  used  for  coal,  ores, 
chemicals,  ashes  and  similar  coarse  materials.  Table  39  gives  weights  and 
dimensions  of  the  regular  sizes. 


Dejection, 


TABLE  39.— MANUFACTURERS'  STANDARD 
MALLEABLE  IRON  BUCKETS— STYLE  A 


Principal  Dimensions,  Inches 

Maximum  Contents 

Weight  of 

Bucket, 

Thickness 

Pounds 

Length 

Projection 

Depth 

on  the  Flat 

Cubic  Inches 

Cubic  Feet 

(Average) 

(see  note) 

4 

2f 

3 

.078 

16 

.009 

.90 

5 

31 

3  f 

.078 

36 

.021 

1.23 

6 

4 

4J 

.093 

55 

.032 

2.15 

7 

4| 

5 

.093 

85 

.049 

2.68 

8 

5 

J5i 

.093 

115 

.066 

3.22 

10 

6 

6; 

.109 

204 

.118 

5.40 

11 

6 

6} 

.109 

223 

.129 

5.61 

12 

6 

6j; 

.109 

246 

.142 

6.53 

12 

7 

7;: 

.140 

332 

.192 

8.78 

14 

7 

7i: 

.140 

391 

.225 

10.90 

14 

8 

8| 

.172 

509 

.294 

13.81 

15 

7 

71 

.140 

425 

.246 

12.30 

16 

7 

7* 

.140 

467 

.270 

13.30 

16 

8 

.172 

593 

.343 

17.54 

18 

8 

8^ 

.172 

668 

.387 

17.80 

18 

10 

10| 

.203 

1053 

.609 

28.20 

23 

7 

n 

.140 

732 

.424 

19.00 

24 

8 

8| 

.172 

887 

.513 

23.00 

NOTE. — Corners  are  50  per  cent  thicker. 

Style  AA  buckets  are  like  A  buckets  with  the  addition  of  metal  to  thicken 
the  digging  edge  and  the  front  corners.  (See  Table  40.) 

Style  B  buckets  hold  less  than  Style  A  buckets  when  compared  on  the 
basis  of  their  contained  volume  in  cubic  inches ;  but  their  carrying  capacity 
in  ordinary  elevators  is  even  less  because,  at  the  speeds  of  centrifugal  dis- 
charge (Table  36)  they  are  apt  to  spill  a  portion  of  their  contents  over  the 


232 


ELEVATOR  BUCKETS 


(Projection 


(_ Length 


TABLE  40.— MANUFACTURERS'  STANDARD 
MALLEABLE  IRON  BUCKETS— STYLE  AA 


Principal  Dimensions,  Inches 

Maximum  Contents 

Weight  of 

Bucket, 

Thickness 

Pounds 

Length 

Projection 

Depth 

on  the  Flat 

Cubic  Inches 

Cubic  Feet 

(Average) 

(see  notes) 

6 

4 

41 

.093 

55 

.032 

2.17 

8 

5 

5£ 

.093 

115 

.066 

3.55 

10 

6 

6| 

.109 

204 

.118 

6.15 

11 

6 

61 

.109 

223 

.129 

6.66 

12 

6 

6i 

.109 

246 

.142 

6.95 

12 

7 

71 

.140 

332 

.192 

9.70 

14 

7 

71 

.140 

391 

.225 

10.55 

14 

8 

8| 

.172 

509 

.294 

16.30 

15 

7 

71 

.140 

425 

.246 

12.40 

16 

7 

71 

.140 

467 

.270 

13  .  08 

18 

8 

8£ 

.172 

668 

.387 

20.24 

20 

8 

8£ 

.172 

720 

.417 

26.50 

24 

8 

8| 

.172 

928 

.537 

26.00 

NOTE  1. — Corners  are  50  per  cent  thicker. 

NOTE  2. — Metal  at  digging  edge  is  double  thickness. 

low  front  lip  (see  p.  213)  if  the  elevator  is  vertical  or  nearly  so  when  the 
bucket  meets  the  head  wheel.  In  inclined  elevators,  when  the  angle  is 
more  than  30°  from  the  vertical,  there  is  some  risk  that  fully  loaded  A 
buckets  will  spill  over  the  top  edge.  This  is  not  so  likely  to  happen  with  B 
buckets,  hence  these  are  sometimes  used  in  such  inclined  elevators.  They  are 
of  greatest  use  in  handling  clay  and  stringy  or  sticky  materials  in  inclined 
elevators.  These  materials  often  stick  in  A  buckets,  but  discharge  more 
readily  from  the  wide-open  mouth  of  B  buckets  at  the  comparatively  low 
speeds  used  in  inclined  elevators. 

Less  than  10  per  cent  of  the  malleable-iron  buckets  sold  in  this  country 
are  Style  B',    A  buckets  are  more  generally  useful  and  will  carry  more 
material  per  dollar  of  investment. 

-i^ >rr*-H"          Table  41   gives  information   about    Style    B 

buckets. 

Style  C  buckets  (see    Table   42)  are   seldom 
used  in  belt  elevators;  they  are  suitable  for  wet 
sugar,  damp  clay  and  similar  materials  too  sticky 
to  discharge  from  A  or  B  buckets. 
FIG.  226. -Cross-section  of         Malleable-iron     Buckets    for    Liquids     and 
17|  by  10-inch  Malleable  Pulps. — In  order  to  prevent   loss   by   splashing 
Iron  Bucket  for   Mineral   out    over    tne    front    lip    at    the    pick-up    or    on 
meeting  the  head  pulley   (see   p.   220)   it   is  an 

advantage  in  high-speed  elevators  to  use  buckets  of  special  form  with  high 
fronts.  Fig.  226  shows  the  cross-section  of  a  17 £  by  10-inch  bucket  used 


SPACING  OF  COMMERCIAL  BUCKETS 


233 


TABLE  41.2-MANUFACTURERS'  STANDARD 
MALLEABLE  IRON  BUCKETS— STYLE  B 


Principal  Dimensions,  Inches 

Maximum  Contents 

Weight  of 

Bucket, 

Thickness 

Pounds 

Length 

Projection 

Depth 

on  the  Flat 

Cubic  Inches 

Cubic  Feet 

(Average) 

(see  note) 

4 

H 

2i 

.062 

6 

.0035 

.41 

7 

3| 

5 

.078 

55 

.032 

1.90 

8 

3^ 

5 

.078 

65 

.038 

2.01 

10 

4 

5£ 

.093 

107 

.062 

3.75 

12 

5^ 

7| 

.109 

233 

.135 

6.95 

16 

6i 

9 

.140 

412 

.238 

13.15 

Ctoigth-^ 
ZJ 


NOTE. — Corners  are  50  per  cent  thicker. 

TABLE  42.— MANUFACTURERS'  STANDARD 
MALLEABLE  IRON  BUCKETS— STYLE  C 


Principal  Dimensions,  Inches 

Maximum  Contents 

Weight  of 
Bucket 
Pounds 
(Average) 

Length 

Projection 

Depth 

Thickness 
on  the  Flat 
(see  note) 

Cubic  Inches 

Cubic  Feet 

6 
7 
8 
10 
12 
14 
16 
18 

4^ 
4s 
4* 

5 
5 

7 
7 
8 

4 
4 
4 
4 
4 
5* 
5| 
8 

.093 
.093 
.093 
.109 
.109 
.140 
.140 
.172 

84 
98 
112 
150 
180 
437 
500 
898 

.049 
.057 
.065 
.087 
.104 
.253 
.289 
.52 

1.93 
2.54 
2.50 
3.75 
3.90 
9.25 
10.80 
17.65 

NOTE. — Corners  are  50  per  cent  thicker. 

at  a  copper  ore  concentrating  works  in  New  Mexico.  Other  sizes  are  also 
made  (see  Table  45,  page  238) ;  these  all  have  very  thick  backs  for  strength 
and  to  resist  the  abrasion  from  fine  material  which  gets  between  the  bucket 
and  the  belt.  The  fronts  are  also  thickened. 

Spacing  of  Commercial  Buckets. — The  parabolas  6  and  7  in  Fig.  202 
represent  the  discharge  of  free-flowing  materials  at  the  speeds  given  in 
Table  35,  and  buckets  spaced  as  shown  in  Fig.  218  might  be  expected  to 
give  a  clean  discharge  so  long  as  the  ratio  of  spacing  to  projection  shown 
there  was  maintained.  In  practice,  however,  it  is  not  advisable  to  space 
smaller  buckets  relatively  so  close  as  the  8  by  8-inch  buckets  shown  in  Fig. 
218;  the  discharge  is  not  quite  so  prompt,  and  so  nearly  radial,  for  several 
reasons.  The  smaller  masses  of  material  discharged  from  the  buckets 


234 


ELEVATOR  BUCKETS 


meet  more  air-resistance,  the  friction  between  the  material  and  the  bucket 
walls  is  relatively  greater  and  the  sheet-steel  buckets  generally  used  in  the 
smaller  sizes  have  bottoms  somewhat  fuller  and  more  rounded  than  the 
Buffalo  buckets.  For  these  reasons,  buckets  smaller  than  8-inch  projection 
must  be  spaced  relatively  further  apart  than  Fig.  218  shows. 

Table  43  gives  closest  spacings  of  sheet-steel  buckets  for  the  elevator 
speeds  given  in  Table  35.  Rialto  buckets  can  be  spaced  close  because 
they  are  shallower  than  other  styles  in  proportion  to  their  projection  and 
hold  less  material. 

TABLE  43.  — FOR  CENTRIFUGAL  DISCHARGE  ELEVATORS  —  CLOSEST 
SPACING  OF  BUCKETS  FOR  FREE-FLOWING  MATERIALS  AT  SPEEDS 
GIVEN  IN  TABLE  35. 


Style 

Projection  of  Bucket 

2 

2£ 

3 

31 

4 

4-1 

5 

4 

6 

8| 

7 

n 

8 

Acme  or  Salem  

5 

6 

7 

8 

9 

10 

11 

12 

12 

13 

14 

15 

16 

Buffalo  
Rialto  

12 
10 

12 
11 

13 
12 

13 

12 

13 
12 

9 

10 

Favorite,  Empire  Com- 
mon Sense,  Seamless  .  . 

10 

11 

12 

13 

13 

14 

15 

16 

18 

MinneaDolis  .  . 

i  to  1  inch  clearance  between  buckets  on  thp  bolt 

For  the  lower  speeds  of  Table  36  buckets  must  be  spaced  farther 
apart.  The  reason  may  be  seen  in  Figs.  202  and  203,  as  compared  with 
Fig.  206.  At  the  lower  speeds  the  discharge  is  more  nearly  tangent  to  the 
sweep  of  the  buckets,  and  more  clearance  is  needed  to  avoid  interference. 
Table  44  gives  closest  spacings  of  buckets  for  the  elevator  speeds  given  in 
Table  36. 

TABLE  44.  — FOR  CENTRIFUGAL  DISCHARGE  ELEVATOR  —  CLOSEST 
SPACING  OF  BUCKETS  FOR  COARSE  OR  GRANULAR  MATERIAL  AT 
SPEEDS  GIVEN  IN  TABLE  36. 


Style 


Projection  of  Bucket 


2 

2J 

3 

3* 

4 

4£ 

5 

*ft 

6 

6^ 

7 

8 

9 

10 

Acme,  Salem  or  any 
of     same     form. 
Malleable  iron,  A, 
AA  or  B  

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

17 

20 

22 

24 

Malleable  Iron  C  .  .  . 

13 

14 

18 

22 

•>8 

PICK-UP  AS  RELATED  TO  SHAPE  OF  BUCKETS  235 

Pick-up  as  Related  to  Shape  and  Spacing  of  Buckets. — In  handling 
lively  free-flowing  material  like  grain  the  buckets  can  be  relatively  close 
together,  because  the  material  flows  into  the  buckets  quickly;  but  for  coal, 
minerals  and  coarse  materials,  the  mickets  must  be  further  apart  to  allow 
time  for  filling.  The  figures  given  in  Tables  43  and  44  are  applicable 
to  most  materials;  but  if  the  buckets  of  a  centrifugal  discharge  elevator 
are  required  to  handle  wet,  stringy  or  sluggish  substances,  it  may  be  neces- 
sary to  space  them  even  farther  apart  than  Table  44  shows.  An  alterna- 
tive is  to  use  an  elevator  of  a  different  type,  one  which  picks  up  the  material 
at  a  slower  speed,  because  vertical  centrifugal  discharge  elevators  cannot  be 
operated  successfully  at  speeds  much  lower  than  those  of  Table  44.  Inclined 
elevators,  perfect  discharge  elevators  on  two  strands  of  chain  and  con- 
tinuous bucket  elevators  will  discharge  at  very  slow  speeds  and  for  some 
materials  they  are  much  more  efficient  than  centrifugal  discharge  ele- 
vators. 

Buckets  with  very  low  fronts,  like  Style  B  malleable-iron  buckets,  will 
not  pick  up  a  full  load  at  speeds  higher  than  Table  44.  They  are  more 
useful  in  slow-speed  elevators  of  other  types,  especially  inclined  elevators. 

Style  C  malleable-iron  buckets  are  not  often  used  in  centrifugal  discharge 
elevators.  When  they  are,  they  must  be  spaced  far  apart  (see  Table  44) 
so  that  the  bottom  does  not  interfere  with  the  discharge  from  the  following 
bucket.  They  will  not  pick  up  at  high  speed. 

Capacities  of  Belt  Elevators. — The  capacities  of  elevators  are  usually 
stated  as  so  many  tons  per  hour,  because  that  is  the  measure  of  the  volume 
of  material  going  through  the  plant  per  hour  or  per  day,  or  the  rate  of 
unloading,  storing,  crushing,  etc.,  in  the  operations  with  which  the  elevators 
are  connected.  So  far  as  the  elevating  capacity  of  the  buckets  is  con- 
cerned, the  material  lifted  in  one  hour  is  sixty  times  the  quantity  lifted  in 
one  minute,  but  that  is  not  always  the  case  in  the  operations  which  the 
elevator  serves.  If  the  supply  to  a  crusher,  mill  or  machine  is  irregular, 
the  feed  to  the  elevator  which  takes  away  from  the  machine  may  for  some 
seconds  or  minutes  be  at  a  rate  much  higher  than  the  hourly  rate  which 
represents  the  working  capacity  of  the  plant.  If  there  are  under  the 
machines  hoppers  or  spouts  large  enough  to  store  the  excess  quantity,  they 
can  be  fitted  with  feeders  or  control  gates  to  regulate  the  feed  to  the  elevator, 
but  most  elevators  are  not  equipped  with  feeding  devices.  Irregularity  of 
supply  to  the  elevator  boot  may  come  also  from  delays  in  car  supply,  inter- 
ruptions in  plant  processes  and  chokes  in  chutes,  which,  when  relieved,  put 
an  increased  burden  on  the  elevator  for  a  time.  See  also  page  148. 

Peak-load  Capacities. — For  the  reasons  stated  above,  elevators  should 
be  designed  for  the  peak-load  or  per-minute  capacity  rather  than  the  average 
or  per  hour  capacity.  Neglect  of  this  precaution  leads  to  trouble  and  dis- 
appointment. An  elevator  seriously  overloaded  for  less  than  a  minute 
may  fail  for  several  reasons. 

1.  If  the  foot  wheel  is  suddenly  buried  in  material,  the  buckets  are  unable 
to  dig  their  way  out,  the  belt  slips  and  the  elevator  stops. 


236  ELEVATOR  BUCKETS 

2.  If  the  supply  to  the  boot  is  beyond  the  elevating  capacity  of  the 
buckets  the  feed  chute  may  fill  up  and  choke. 

3.  When  the  elevator  belt  slips,  its  speed  falls  off  to  the  point  at  which 
the  buckets  do  not  make  a  clean  discharge,  the  spill  falls  down  the  back  leg 
and  adds  to  the  accumulation  in  the  boot,  and  the  elevator  stops. 

There  are  many  belt  elevators  in  service  which  are  large  enough  to 
give  the  required  number  of  tons  per  hour  with  regular  feed  and  steady 
operation,  but  too  small  to  handle  the  load  as  it  is  delivered  to  the  boot 
per  minute.  Such  elevators  have  trouble  with  chokes,  belts  worn,  torn  or 
dried  out  by  repeated  slipping,  pulley  lagging  worn  off,  buckets  tearing  off, 
and  the  annoying  delays  and  expense  of  shut-downs  and  repairs. 

Bucket  Capacity  and  Elevator  Capacity. — Under  favorable  conditions 
of  pick-up  and  discharge,  the  capacity  of  an  elevator  in  pounds  per  minute 
equals 

Bucket  capacity  in  pounds  X  Belt  speed  in  feet  per  minute 
Bucket  spacing  in  feet 

but  where  the  bucket  does  not  pick  up  a  full  load  or  discharge  clean,  the 
capacity  is  less.  For  reasons  given  in  Chapter  XV,  buckets  in  centrifugal 
discharge  elevators  take  a  full  load  only  when  the  belt  speed  and  diameter 
of  foot  pulley  are  correctly  related  and  when  the  boot  is  of  the  right  shape. 
In  many  elevators  these  favorable  conditions  do  not  exist,  the  pulleys  in 
the  boot  are  too  small,  the  loading  is  too  low  and  the  buckets  go  up  partly 
empty. 

Manufacturers'  catalogues  rate  buckets  by  their  contents  in  cubic  inches; 
^4  this  is  the  contained  volume  measured  to  the  line  A  A 

(Fig.  227),  but  for  reasons  stated  above,  buckets  in 
centrifugal  discharge  elevators  do  not  usually  fill  to 
that  line.      In  high-speed   grain  elevators   when  the 
conditions  of  loading  and  discharge  are  favorable  it  is 
proper  to  deduct  10  to  15  per  cent  in  calculating  the 
FIG.  227.  —  Theoreti-    lifting  capacity  of  the  bucket.     If  the  feed  is  such  that 
cal  Filling  of  Ele-    ±ne   buckets    can   not    complete   their   loading   at  or 
above  the  level  of  the  foot  shaft,  the  deduction  should 
be  greater  than  15  per  cent. 

Grain  elevator  buckets  run  at  the  speeds  of  Table  36  over  good-sized 
foot  wheels  are  likely  to  fill  within  10  per  cent  of  nominal  capacity. 

In  ordinary  centrifugal  discharge  elevators  for  coal,  ores  and  minerals 
the  buckets  should  not  be  expected  to  carry  more  than  75  per  cent  of  their 
rated  capacity.  If  the  feed  is  too  low  or  the  foot  wheel  too  small,  the 
capacity  will  not  reach  75  per  cent. 

When  inclined  elevators  are  run  at  the  speeds  of  Tables  36  or  37  the 
pick-up  is  good  and  the  buckets  may  load  to  nearly  full  capacity  if  the 
inclination  is  between  20°  and  30°  from  the  vertical. 

When  buckets  dig  from  an  open  pile,  filling  will  not  average  over  50 
per  cent  of  nominal  capacity. 


EUROPEAN  BUCKETS  FOR  FLOUR  AND  GRAIN 


237 


In  handling  liquids  or  mineral  pulps  at  the  speeds  of  Tables  35  or  36  it  is 
hardly  safe  to  count  on  the  buckets  in  vertical  elevators  loading  more  than 
one-third  full.  Inclined  elevators  aj^  the  speeds  of  Table  36  will  carry  more, 
especially  with  a  large  foot  wheel. 

Examples. — Buffalo  buckets,  15  by  8  by  8  inches,  rated,  at  581  cubic 
inches,  used  in  a  high-speed  elevator,  never  carried  more  than  14  pounds 
of  wheat  in  service.  This  is  equivalent  to  537  cubic  inches,  a  loss  of  14 
per  cent  in  capacity. 

In  tests  of  a  well-designed  elevator  for  pulverized  ore,  with  14  by  8-inch 
malleable  iron,  Style  A  buckets,  the  contents  averaged  400  cubic  inches  per 
bucket,  a  reduction  of  21  per  cent  from  the  nominal  capacity  of  509  cubic 
inches. 

Table  45  gives  facts  about  belt  elevators  in  use  in  a  copper  smelter  in 
New  Mexico,  most  of  them  in  wet  service.  The  nominal  capacities  in  the 
last  line  of  the  table  are  calculated  on  the  assumption  that  every  bucket 
takes  a  full  load  for  every  minute  of  the  twenty-four  hours.  The  great 


FIG.  228.  FIG.  229.  FIG.  230.  FIG.  231. 

EUROPEAN  BUCKETS  FOR  GRAIN  ELEVATORS. 

FIG.  228. — "Deep-pressed"  Bucket. 

FIG.  229. — ' '  Shallow-pressed  "Bucket. 

FIG.  230. — One-piece  V  Bucket  with  Rounded  Bottom. 

FIG.  231. — Two-piece  V  Bucket  with  Sharp  Bottom. 

margin  between  these  figures  and  the  actual  capacities  in  ore,  over  and  above 
the  water  handled,  represents  allowances  for  various  items:  (1)  some 
irregularity  in  ore  supply;  (2)  loss  of  time  in  shut-downs;  (3)  imperfect 
filling  of  buckets;  (4)  some  spill  on  the  lift  and  at  the  discharge  into  the 
head  chute;  (5)  using  throughout  the  mill,  belts  and  buckets  of  standard 
sizes  (that  is,  standard  for  that  mill).  This  brings  about  a  desirable  uni- 
formity among  the  elevators,  although  some  are  much  too  large  for  the  work. 
European  Buckets  for  Flour  and  Grain. — The  ordinary  "  deep-pressed  " 
bucket  used  in  Europe  is  a  one-piece  sheet-steel  bucket  similar  to  the 
Salem  or  Acme,  and  has  a  top  angle  of  about  70°  and  a  bottom  angle  of 
about  33°  (Fig.  228).  The  "  shallow-pressed  "  bucket  is  similar  in  con- 
struction to  the  "  deep-pressed  "  bucket,  but  it  does  not  match  any  Amer- 
ican bucket  in  shape.  It  has  a  bottom  angle  of  about  60°  and  the  top 
angle  measured  from  the  back  edge  to  the  front  lip  is  also  about  60°;  but 
the  tops  of  the  sides  are  carried  up  higher  than  the  straight  line  which 
measures  the  top  angle  (Fig.  229).  This  bucket  has  several  merits: 


238 


ELEVATOR  BUCKETS 


xx     * 


,  Q 


i    s 


PS 

CO 


^  &! 

^§  S 


rse 


Coa 

Crushing 
Departme 


E 


S  E-1  cS 


EUROPEAN  BUCKETS  FOR  FLOUR  AND   GRAIN 


239 


1.  In  handling  flour,  bran  or  light  mill  products  it  will  fill  better  because 
it  has  a  wide-open  mouth  and  tha  air  can  get  out  of  the  bucket  and  the. 
material  get  into  it  without  stirring^p  so  much  dust. 

2.  On  account  of  the  high  ends  it  will  carry  more  material  than  if  the 
ends  were  cut  off  straight,  as  is  usual  in  American  buckets. 

3.  On  account  of  the  straight-line  front  and  the  large  bottom  angle  it 
will  discharge  light  mill  products  readily,  and  for  the  same  reason  there 
is  a  clean  discharge  of  flour  which  tends  to  pack  into  small  angles  and  sharp 
corners  of  buckets  of  some  other  styles.     The  low-front  sheet-steel  buckets 
of  American  makers  generally  have  more  of  the  front  cut  away;   the  top 
angle  is  therefore  small  and  the  bucket  will  discharge  readily;    but  the 
carrying  capacity  is  unnecessarily  reduced  for  such  substances  as  those 
mentioned,  and  for  which  sheet  steel  or  tin  buckets  are  in  general  use. 

Buckets  of  angular  form,  like  the  Minneapolis  bucket,  are  quite  popular 
in  Europe.  They  are  made  in  one-piece  style  (Fig.  230)  with  a  small  fillet 
in  the  lower  corner,  or  in  two  pieces  with  the  bottom  sheet  separate,  flanged 
and  riveted  to  the  ends  (Fig.  231),  in  which  case  the  bottom  corner  is  sharp. 


FIG.  232.  FIG.  233.  FIG.  234. 

FIG.  232. — European  Bucket  for  High-speed  Grain  Elevator. 
FIG.  233. — "Funnel"  Buckets  for  High-speed  Grain  Elevator. 
FIG.  234. — High-speed  Grain  Elevator  Bucket,  set  Continuous  on  the  Belt. 

Fig.  232  shows  still  another  form  of  this  bucket  (U.  S.  patent  665273  of 
1901)  in  which  the  lower  edge  of  the  front  sheet  is  flanged  and  bears  against 
the  belt  as  a  prop  for  the  bucket.  In  all  of  these,  the  lower  edge  of  the 
front  must  come  close  to  the  back,  so  that  the  discharge  from  the  following 
bucket  will  either  clear,  or  be  deflected  by,  the  front  sheet. 

European  makers  list  sheet-steel  buckets  with  a  flat  back  and  a  kind  of 
half-conical  front  (Fig.  233).  These  will  dig  through  a  deep  mass  of  grain 
in  a  boot  more  easily  than  buckets  of  any  other  shape;  they  are  light  and 
strong  and  discharge  well  at  speeds  even  higher  than  those  of  Table  35. 
They  can  be  set  with  little  clearance  on  the  belt  and  will  not  interfere  with 
the  discharge.  A  bucket  of  this  style  10  inches  wide,  7j-inch  projection 
holds  .16  cubic  foot;  at  10-inch  spacing  this  is  equivalent  to  .19  cubic  foot 
per  foot  of  belt.  By  comparing  this  with  Table  38,  page  230,  and  halving 
the  figures  of  the  latter  for  a  bucket  10  inches  wide,  it  is  evident  that  these 
so-cajled  "  funnel  "  buckets  will  give  a  large  capacity. 

A  similar  bucket  with  a  pyramidal  bottom,  and  made  from  one  piece 
of  sheet  steel,  is  shown  in  Fig.  234.  It  is  covered 'by  U.  S.  patent  788590 
of  1905. 


CHAPTER  XVII 


CONTINUOUS  BUCKET  ELEVATORS 


Continuous  Bucket  Elevators. — When  buckets  of  the  shape  shown  in 
Fig.  201  are  set  close  together  on  a  belt  they  empty  by  a  pouring  action 
and  do  not  need  the  throw  imparted  by  high  centrifugal  force.  Hence 
they  can  be  run  at  comparatively  slow  speeds  with  merely  enough  velocity 
to  dislodge  the  material  from  the  bucket,  to  avoid  dribble  into  the  gap 
between  the  buckets  and  to  assist  the  discharge  to  flow  promptly  over  the 
bottom  of  the  leading  bucket. 

Pick-up  and  Discharge. — The  bolts  which  fasten 
the  back  of  a  bucket  to  a  belt  must  necessarily  be  in 
one  or,  at  most,  two  rows  so  as  to  allow  the  belt  to  bend 
on  the  pulleys  (see  p.  256).  In  fastening  the  com- 
paratively shallow  and  round-bottomed  buckets  used  in 
centrifugal  discharge  elevators,  the  bolts  are  near  the 
top  of  the  back  edge,  but  with  the  deeper  and  heavier 
buckets  used  in  continuous  bucket  elevators,  the  bolts 
must  be  about  half-way  between  top  and  bottom  in 
the  back  plate.  In  Fig.  235  the  top  half  of  diagram  A 
represents  continuous  buckets  bolted  near  the  top  edge, 
passing  over  the  top  of  a  pulley,  while  the  bottom  half 
shows  the  action  under  a  foot  pulley.  The  pick-up 
under  the  pulley  might  be  called  good,  but  the  dis- 
charge is  bad,  because  material  will  be  poured  out  of 
one  bucket  into  the  space  between  the  belt  and  the 
bucket  ahead.  In  diagram  B,  showing  buckets  bolted 
at  the  bottom,  the  pick-up  is  bad,  because,  material 
will  enter  the  gap  between  belt  and  bucket,  but  the 
discharge  is  good.  If  the  buckets  are  fastened  at  the 
middle,  according  to  standard  practice  (see  diagram  C), 
the  result  is  a  compromise;  the  gap  which  opens 
FIG.  235.  —  Pick-up  between  the  belt  and  bucket  is  relatively  small  and 
Conti^iousBuckets  at  the  digcharge  point  material  is  not  likely  to  get  into 
as  Affected  by  it  unless  the  speed  is  so  slow  that  the  contents  of  the 
bucket  dribble  out.  Material  would  get  into  the  gap 
if  the  bucket  picked  up  its  load  from  a  boot;  for  that 
reason,  belt  elevators  of  this  kind  should  never  be  loaded  from  a  boot,  but 
from  a  chute  (Fig.  236)  at  a  point  above  the  foot  pulley  where  the  buckets 

240 


Method  of  Fasten- 
ing to  Belt. 


SHAPE  OF  CONTINUOUS  BUCKETS 


241 


FIG.  236. — Loading  and  Discharging  Con- 
tinuous Bucket  Elevator. 


are  on  the  straight  run,  lie  close  to  the  belt  and  do  not  present  any  gap 
into  which  material  might  enter.,   When  material   does   get  between  the 
belt  and  the  back  of  the  bucket  it  igay  wedge  tight  there  and  put  a  severe 
strain  on  the  bolt  fastening,  and  is 
apt  to  wear  or  punch  holes  in  the  belt 
from  repeated  pressure  in  going  over 
the  pulleys. 

The  distance  x  (Fig.  236)  from 
the  lower  edge  of  the  loading  chute 
to  the  shaft  in  its  upper  position  of 
take-up  travel  should  be  at  least  equal 
to  the  height  of  one  bucket;  more  is 
preferable,  to  make  sure  that  the 
bucket  A  will  catch  all  that  B  misses, 
and  that  A  is  flat  against  the  belt 
when  the  feed  pours  into  it.  At  the 
head,  the  upper  edge  of  the  discharge 
chute  is  usually  set  at  45°  below  the 
level  of  the  head  shaft  and  as  close 
to  the  elevator  as  the  sway  and  move- 
ment of  the  buckets  will  permit;  then 
if  the  buckets  are  properly  shaped  and 
run  at  proper  speed,  stone,  coal,  gravel 

and  such  materials  handled  in  continuous  bucket  elevators  will  flow  out  in 
a  clean  discharge.  If  the  material,  gravel,  for  instance,  is  quite  wet  and 
contains  sand,  it  is  better  to  put  the  chute  lower  by  a  foot  or  two  to  catch 
the  delayed  discharge  and  the  drip. 

Shape  of  Continuous  Buckets. — In  Fig.  236  the  contents  of  C  are  pouring 
out  over  the  bottom  of  D,  and  it  is  evident  that  a  clean  and  prompt  delivery 
to  the  chute  depends,  among  other  things,  on  the  angle  at  which  the  bottom 
of  D  stands  at  the  moment  it  acts  as  a  chute.  In  most  continuous  bucket 
elevators  there  is  some  "  throw  "  which  helps  material  across  D  to  the 
chute,  and  some  of  the  discharge  may  enter  the  chute  without  touching  D 
at  all;  nevertheless,  there  is  always  some  spill  onto  the  bottom  of  D  which 
must  slide  off. 

In  order  to  make  the  angle  F  (Fig.  236)  steep  enough  to  let  material 
slide  easily,  the  bucket  must  have  the  right  shape;  the  angle  G  in  the 
bottom  must  bear  a  proper  relation  to  the  material  handled  and  to  the 
angle  H  representing  the  deflection  of  the  bucket  from  the  vertical  at  the 
position  D.  If  the  elevator  stands  vertical  H  is  zero  and  (7=90°  — .F; 
if,  for  instance,  the  material  is  clean  and  fairly  dry,  it  will  flow  on  a  steel 
plate  when  7^=40°;  then  the  bucket  should  have  a  bottom  angle  of  50°. 
It  is  generally  better  to  have  G  larger  than  50°,  so  that  material  will  not  be 
so  likely  to  wedge  in  the  bottom  corner,  and  since  gravel,  damp  coal,  stone, 
dust  and  similar  substances  flow  more  readily  when  F  is  45°,  it  is  an  advan- 
tage to  incline  the  elevator  so  that  H  is  at  least  10°.  For  this  condition 


242 


CONTINUOUS  BUCKET  ELEVATORS 


£  =  #+90°-^  or  100+90°-45°=550.  If  the  elevator  has  a  greater 
inclination  from  the  vertical,  H  might  be  15°,  then  the  buckets  could  have  a 
bottom  angle  G  of  60°.  The  angle  H  can  be  taken  from  Table  57;  strictly 
considered,  the  angles  B  in  that  table  refer  to  belts  without  applied  tension; 
when  take-up  tension  is  applied,  B  becomes  less  and  H  greater,  but  for 
practical  purposes,  the  table  may  be  used  and  H  may  be  considered  equal 
to  90° -B. 

Based  on  these  considerations,  as  well  as  those  referring  to  the  loading, 
most  continuous  bucket  elevators  on  belt  are  inclined  from  15°  to  30°  from 
the  vertical  and  have  buckets  with  the  bottom  angle  G  from  50°  to  60°. 
Some  buckets  are  made  with  G  equal  to  70°,  but  they  do  not  give  a  clean 
discharge  unless  the  elevator  is  inclined  at  least  25°  from  the  vertical  and 
handle  dry,  clean,  free-flowing  material.  For  that  case,  H  is  about  10° 
or  12°  and  F=  30°  or  32°. 

From  a  consideration  of  the  way  the  feed  enters  the  bucket  from  the 
loading  chute  (Fig.  236)  it  is  evident  that  the  buckets  must  be  open  in  front. 
They  would  hold  more  if  made  with  a  short  front  sheet  parallel  to  the  back 
sheet,  but  such  a  front  would  interfere  with  the  loading,  would  splash  and 
spill  the  material  and  would  soon  wear  out. 

Fig.  237  shows  various  shapes  of  continuous  buckets,  No.  1  being  the 
ordinary  two-piece  bucket,  one  sheet  forming  the 
back  and  ends,  another  sheet,  flanged  at  each  end, 
forming  the  bottom.  The  corresponding  three-piece 
bucket,  No.  2,  has  two  end  pieces  riveted  to  one  sheet 
which  makes  the  back  and  bottom.  In  order  to  pre- 
vent scatter  and  spill  at  the  loading  chute,  buckets 
are  sometimes  made  like  No.  3  or  No.  4,  but  they  have 
given  trouble  at  times,  by  stones  catching  between 
the  end  plates  of  adjacent  buckets,  and  the  projecting 
corners  of  the  end  plates  are  apt  to  be  knocked  out  of 
shape  in  handling  heavy  material.  These  mishaps  are 
not  likely  to  happen  with  buckets  like  No.  1  and  No.  2, 
because  the.  end  plates  do  not  butt  against  each  other 
and  the  corners  have  been  trimmed  off.  Buckets  like 
No.  5  have  been  made  with  the  idea  of  improving 
the  discharge,  as  where  C  discharges  onto  the  back  of 
D  (Fig.  236).  The  overlapping  end  plates  confine  the 
discharge  and  prevent  it  from  scattering,  but  in  course 
of  time  the  overhanging  corners  of  the  plates  are 
likely  to  get  out  of  shape  and  then  spoil  the  overlap, 
or  interfere  with  each  other.  Buckets,  in  end  view 
like  No.  2  or  No.  4,  are  sometimes  made  tapering,  narrower  at  the  top 
than  at  the  bottom  so  as  to  overlap  and  thus  prevent  the  discharge  from 
spreading  out  too  far  sideways.  They  have  some  advantage  in  that  respect, 
but,  on  the  other  hand,  loading  is  not  so  likely  to  be  clean  as  when  the  end 
plates  of  the  buckets  are  all  in  one  plane,  that  is,  not  tapered. 


FIG.  237.— Some  Forms 
of  Continuous  Buck- 
ets. 


HEIGHT  OF  BUCKET  AND  DIAMETER  OF  PULLEY 


243 


Height  of  Bucket  and  Diameter  of  Pulley. — In  order  that  the  bucket 
may  not  gap  away  from  the  belt  tqo  far  (see  diagram  C,  Fig.  235)  the  bucket 
must  not  be  too  high,  measured  alo^g  the  belt,  nor  must  the  pulley  be  too 
small.  Table  46  gives  tKe  amount  of  the  gap  in  inches,  measured  radi- 
ally, for  various  heights  of  buckets  and  diameters  of  pulleys.  The  gap 
should  never  be  more  than  one-eighth  the  height  of  the  bucket,  and  therefore 
combinations  to  the  left  of  the  heavy  line  in  the  table  should  not  be  used. 

TABLE  46.— RELATION  OF  HEIGHT  OF  BUCKET  TO  DIAMETER 

OF  PULLEY 


Height 
of  Bucket, 
Inches 

Gap  Between  Belt  and  Bucket,  Inches 

Diameter  of  Pulley,  Inches 

18 

24 

30 

36 

42 

48 

8 
10 
12 
14 
16 
18 

.84 
1.29 

.64 
1.00 

1.41 

.52 

.81 
1.15 
1.55 
2.00 

.43 
.68 
.97 
1.31 
1.69 
2.12 

.37 

.58 
.84 
1.13 
1.47 
1.84 

.33 
.51 
.73 
1.00 
1.29 
1.63 

1.81 
2.40 
3.04 
3.72 

1.82 
2.42 
3.00 

2.49 

Buckets  more  than  16  inches  high  are  seldom  used,  even  with  large  pul- 
leys; it  is  hard  to  fasten  them  securely  to  the  belt  with  two  or  even  three 
rows  of  bolts. 

Capacities  of  Continuous  Buckets. — It  is  not  possible  to  give  rules  for  the 
carrying  capacities  of  continuous  buckets.  The  loading  chute  is  always 
narrower  than  the  bucket  and  the  ends  do  not  fill  so  well  as  the  middle  of 
the  bucket.  The  amount  that  can  be  piled  in  a  bucket  depends  on  the  piling 
angle  of  the  material,  the  shape  of  the  front  of  the  bucket  and  the  inclination 
of  the  elevator;  but  it  does  not  usually  exceed  75  per  cent  of  the  maximum 
represented  by  the  cubic  contents  of  the  bucket.  It  is  generally  necessary 
to  make  a  sketch  to  determine  the  carrying  capacity. 

Speeds  of  Continuous  Bucket  Elevators. — On  the  use  of  continuous 
buckets  for  elevating  grain  at  high  speed,  see  page  226.  Generally  the 
term  "  continuous  bucket  elevator  "  is  applied  to  machines  that  run  at 
speeds  lower  than  those  of  Table  36  and  which  do  not  depend  altogether 
on  centrifugal  force  to  empty  the  buckets.  The  low  limit  of  speed  is  that 
which  will  prevent  material  from  dribbling  into  the  gap  between  the  buckets 
(see  p.  244),  and  the  high  limit  is  determined  by  the  nature  of  the  material 
and  the  delivery  to  the  buckets.  Such  elevators  on  belt  are  seldom,  if  ever, 
used  to  pick  up  material  from  a  boot  because  of  the  danger  that  material 
will  crowd  between  the  belt  and  the  bucket,  pack  there,  and  pull  the  bolts 
through  the  belt  or  tear  the  buckets  off.  When  they  are  fed  from  a  chute 
at  some  distance  above  the  foot  wheel,  as  they  should  be  (see  p.  241),  the 


244  CONTINUOUS  BUCKET  ELEVATORS 

considerations  are  that  the  bucket  should  have  sufficient  time  to  fill  prop- 
erly, and  that  the  impact  of  the  material  delivered  to  the  bucket  should  not 
be  too  severe  for  the  fastening  to  the  belt.  If  the  material  is  large  in 
proportion  to  the  area  of  cross-section  of  the  bucket,  or  if  the  pieces  are  long 
and  flat,  like  shale  or  some  kinds  of  crushed  cement  rock,  the  load  does  not 
settle  quickly  into  position  in  the  bucket  and  a  relatively  slow  speed  is 
necessary  to  load  the  bucket  properly  and  avoid  spill  over  the  front  edge. 
Elevators  that  handle  such  material  may  be  run  between  100  and  150  feet 
per  minute. 

Speed  Must  Not  Be  Too  Low. — In  handling  materials,  like  moist  fine 
ores  or  excavated  earth  or  other  substances  which  do  not  flow  readily  on 
themselves,  continuous  buckets  may  fill  with  a  high  surcharge.  In  passing 
over  the  head  pulley  the  surcharge  will  spill  into  the  gap  between  the 
buckets,  unless  the  speed  is  high  enough  to  influence  the  discharge  by 
centrifugal  action.  For  such  conditions  it  is  advisable  to  use  belt  speeds 
as  high  as  those  of  Table  37,  page  220. 

Objections  to  High  Speed. — If  the  material  is  small,  like  crushed 
slag  or  stone  for  road  building,  railroad  ballast  or  concrete  construc- 
tion, the  speed  may  be  higher  without  much  risk  of  spill  and  scant 
loading.  Two  hundred  feet  per  minute  has  been  considered  standard 
for  such  work,  but  there  are  many  belt  elevators  running  at  higher 
speeds  which  are  thought  to  be  satisfactory.  In  some  cases  the  belt 
travels  as  fast  as  300  feet  per  minute;  the  object,  of  course,  is  to 
get  a  high  capacity  from  a  belt  and  bucket  of  given  size.  Some  of  these 
elevators  handle  small  stuff,  relatively  light  in  weight,  like  crushed  slag, 
satisfactorily;  but  there  are  others  carrying  heavy,  coarse  materials,  where 
the  high  speed  causes  an  excessive  amount  of  spill  and  unusual  wear  and 
tear  on  the  belt  and  buckets.  Buckets  15  inches  high  traveling  300  feet 
per  minute  pass  a  loading  chute  at  the  rate  of  four  per  second.  Considering 
the  depth  of  material  in  the  loading  chute,  the  time  of  loading  such  a 
bucket  is  perhaps  as  much  as  one-third  of  a  second,  certainly  no  more.  This 
may  be  sufficient  for  fine  material  to  run  into  and  fill  a  bucket,  but  not  so 
with  coarse  stuff.  There  are  many  elevators  handling  stone  2  inches  and 
larger  where  the  buckets  do  not  take  a  full  load  and  where  the  capacity 
elevated  would  be  greater  if  the  belt  speed  were  less.  Lower  speed  means 
better  filling,  less  spill  and  scatter  into  the  pit  at  the  foot  of  the  elevator 
and  less  pull  on  the  bucket  bolts  at  the  loading  point  and  in  going  under  the 
foot  wheel  and  over  the  head  wheel. 

Sizes  of  Pulleys. — For  reasons  given  in  Chapter  V  and  Chapter  XX 
the  diameter  of  head  pulleys  should  be  at  least  5  inches  per  ply  of  belt. 
Pulleys  smaller  than  this  do  not  grip  the  belt  so  well,  and  the  belt  wears 
out  sooner  because  of  slip  or  by  reason  of  excessive  stress  on  the  friction 
rubber  or  the  stitching  which  holds  the  plies  together. 

Loading  Legs  for  Continuous  Bucket  Elevators. — In  order  to  reduce  the 
amount  of  spill  and  scatter,  continuous  buckets  are  sometimes  run  between 
side  boards  or  plates  at  the  loading  point,  or  the  two  sides  may  be  joined 


LOADING  LEGS  FOR  CONTINUOUS  BUCKET  ELEVATORS     245 

by  a  front  sheet  below  the  loading?  chute  so  as  to  form  a  three-sided  box 
a  few  feet  deep.  In  some  cases  these  have  worked  well,  but  in  others  they 
have  been  tried  and  then-thrown  6rit.  In  stone  elevators,  the  material  is 
apt  to  get  into  the  clearance  spaces  between  the  moving  buckets  and  the 
fixed  plates,  and  either  wear  out  the  plates  or  damage  the  buckets  and  the 
belt.  The  fastening  of  a  continuous  bucket  to  a  belt  is  necessarily  confined 
to  a  number  of  bolts  that  perforate  a  narrow  strip  across  the  width  of  the 
belt;  anything  that  puts  an  added  strain  on  this  section  of  the  belt  is  to 
be  avoided.  If  the  loading  chute  is  properly  sloped  and  set  with  reference 
to  the  buckets,  and  if  the  belt  speed  is  not  too  great,  the  amount  of  spill  is 
ordinarily  not  objectionable.  In  most  cases  it  is  better  to  clear  away  the 
spill  regularly  rather  than  try  to  prevent  it  by  the  use  of  a  loading  leg. 

For  further  information  about  inclined   continuous  bucket  elevators 
see  Chapter  XXII.     Refer  also  to  Chapters  XVIII  and  XX. 


CHAPTER  XVIII 
BELTS  FOR  ELEVATORS 

Belts  for  Elevators. — So  far  as  materials  of  construction  and  methods 
of  manufacture  are  concerned,  elevator  belts  are  like  conveyor  belts,  and 
what  is  said  in  Chapter  III  applies  generally  to  belts  for  elevating  as  well 
as  for  conveying. 

Elevator  service  may  be  considered  an  extension  of  conveyor  service; 
a  belt  will  convey  certain  material  on  the  level  or  on  any  slope  up  to  20°; 
fitted  with  cleats  to  prevent  the  material  from  rolling  or  sliding,  it  will  carry 
up  to,  say,  30°;  fitted  with  buckets  to  hold  the  material  it  will  carry  at  any 
angle  up  to  the  vertical. 

There  are  some  features  of  elevator  service  which  make  that  work 
harder  for  belts  than  conveyor  service : 

1.  Most  elevators   are   under   75-foot   centers,  very  few  are  over  150- 
foot  centers;    they  are  shorter  than  conveyors,  and  since  the  speeds  are 
not  much  different,  the  belt  makes  more  contacts  with  the  pulleys  and  is 
bent  oftener. 

2.  Elevator   pulleys,   especially  foot   pulleys,   are   apt  to   be  smaller, 
considering  the  number  of  belt  plies,  than  corresponding  pulleys  on  con- 
veyors;   the  tendency  to  stretch  or  break  the  bond  between  the  plies  of 
fabric  is  therefore  greater. 

3.  The  unit  stress  in  the  belt,  that  is,  the  pounds  pull-  per  inch  per  ply 
is  often  greater  in  an  elevator  belt  than  in  a  conveyor  belt  (see  p.  209). 

4.  Elevator  belts  are  subject  to  cutting  and  wear  on  the  outer  side  from 
material  delivered  against  it  by  feed  chutes  or  in  the  boot;  they  are  cut  by 
the  top  edge  of  the  back  of  the  bucket  and  worn  by  bits  of  material  caught 
between  the  belt  and  the  bucket.     On  the  pulley  side  they  are  often  gouged 
and  torn  by  the  heads  of  the  bucket  bolts  or  by  material  falling  between  the 
belt  and  the  foot  pulley.    Belt  creep  and  belt  slip  wear  the  belt  (see  p.  276) 
by  rubbing  on  the  head  pulley;   the  same  thing  happens  when  dirt  and  grit 
adhere  to  the  pulley  side  of  the  belt;   water  enters  through  the  bolt  holes 
and  destroys  the  cotton  fiber  and  the  bond  between  the  layers  of  fabric. 

5.  A  conveyor  does  its  work  in  the  open;   the  manner  of  loading  can  be 
seen  and  the  condition  of  the  belt  observed.     An  elevator  is  usually  enclosed 
and  the  pick-up  is  not  visible.     It  often  happens  that  loose  buckets  and 
loose  bolts  are  not  noticed  in  time  to  prevent  damage  to  the  belt. 

6.  An  overloaded  conveyor  belt  gives  warning  by  spilling  the  excess  over- 
the  sides  where  it  can  be  seen.     A  choke  in  an  elevator  boot  is  usually 
hidden  from  view;   it  may  cause  the  belt  to  slow  down  or  stop  and  before 

246 


GRAIN  ELEVATOR  BELTS  247 

the  drive  can  be  stopped,  the  head  pulley,  continuing  to  turn,  may  damage 
the  belt  or  wear  it  through.  *  :  /' 

7.  Elevator  belts  are  more  Easily  overloaded  than  conveyor  belts. 
The  normal  ratings  of  conveyor  belts  are  about  one-half  the  maximum 
loading  (see  Fig.  137).  Elevator  capacities  are  often  calculated  from  the 
cubic  capacity  of  the  buckets  as  given  in  manufacturers'  catalogues.  These 
may  be  realized  if  the  pick-up  is  good,  but  where,  as  often  happens,  the 
foot  wheel  is  too  small  or  the  boot  is  not  suited  to  the  material  handled, 
the  buckets  do  not  take  a  full  load.  It  is  a  matter  of  observation  that  an 
elevator  with  a  steady  feed  to  the  boot  will  run  with  a  series  of  buckets  only 
partly  full;  then  as  the  accumulation  in  the  front  of  the  boot  piles  up  to  the 
center  of  the  foot  wheel  or  higher,  the  buckets  fill  full  for  some  seconds; 
then  the  loading  falls  off  again  and  the  cycle  is  repeated.  The  result  is 
that  the  capacity  of  the  elevator  is  less  than  what  was  calculated,  and  the 
margin  between  the  actual  and  the  calculated  capacity  may  be  so  little  that 
a  slight  excess  of  feed  is  apt  to  choke  the  elevator,  with  resulting  injury  to 
the  belt. 

The  first  belt  elevators  were  used  for  grain  in  flour  mills;  in  recent  years 
their  use  has  been  extended  to  practically  all  kinds  of  elevating  work  except 
dredging. 

Grain  Elevator  Belts. — Oliver  Evans,  in  his  "  Miller's  Guide,"  published 
in  Philadelphia  in  1795,  describes  as  one  of  his  inventions,  what  was  then  a 
new  thing,  at  least  to  the  milling  business,  i.e.,  an  elevator  composed  of  a 
leather  belt  with  cups  or  buckets  fastened  on  at  intervals  and  discharging 
their  contents  by  centrifugal  action  over  the  upper  pulley.  To  handle  300 
bushels  per  hour,  the  elevator  consisted  of  a  strap  of  harness  leather  4£  inches 
wide  with  buckets  holding  1  quart  strapped  on  to  the  belt  every  15  inches. 
The  head  pulley  was  24  inches  in  diameter  and  made  about  30  revolutions 
per  minute.  The  foot  pulley  was  smaller  and  was  contained  in  a  wooden 
boot  which  was  part  of  a  wooden  casing  with  double  legs.  The  buckets 
were  of  willow  wood  |  inch  thick,  steamed  and  bent  to  form  the  front  and 
ends;  a  piece  of  leather  tacked  on  formed  the  bottom,  and  the  elevator  belt 
acted  as  the  back,  the  elevator  being  inclined  15°  or  20°  from  the  vertical. 
Evans  showed  also  how  to  make  buckets  of  sheet  iron,  but  that  material 
was  scarcer  than  willow  wood  in  the  United  States  in  1785,  when  the  first 
of  these  elevators  was  built. 

Evans  and  his  successors,  Ellicott  and  others,  built  many  belt  elevators 
in  flour  mills  up  to  1830;  in  1842  when  Joseph  Dart  built  the  first  bulk 
storehouse  ("  elevator  ")  for  grain  on  the  Great  Lakes  at  Buffalo,  it  had  a 
belt  elevator  of  1000  bushels  per  hour  capacity.  By  1866  many  "  elevators  " 
had  been  built  at  Cleveland,  Toledo,  Chicago,  Milwaukee  and  other  Lake 
ports,  some  of  them  holding  over  a  million  bushels.  The  first  "  elevator  " 
on  the  Atlantic  coast  was  erected  in  Philadelphia  between  1859  and  1863; 
it  had  e'evators  with  leather  belts  20  inches  wide  and  |  inch  thick.  Rubber 
belts  came  in  about  1870  and  became  popular  during  the  rapid  building  of 
grain  "  elevators  "  in  this  country  during  the  seventies  and  eighties.  Some 


248  BELTS  FOR  ELEVATORS 

of  these  belts  were  of  excellent  quality  (see  p.  30),  but  as  to  their  construc- 
tion, the  specifications  for  the  early  elevators  give  little  information; 
those  for  the  Pennsylvania  Railroad  Company's  Girard  Point  Elevator 
in  Philadelphia  in  1881  merely  call  for  "  best  quality  smooth-surface  gum 
belts." 

With  the  growth  of  the  business  came  the  detailed  specification  for 
rubber  belts,  such  as  the  well-known  Metcalf  specification  (see  p.  31). 
This  specification  and  others  similar  to  it  are  still  in  use;  but  as  has  been 
stated  (p.  37),  there  is  a  growing  dependence  upon  the  quality  which 
experienced  manufacturers  have  put  into  their  trade-marked  belts  and  less 
insistence  upon  some  of  the  details  of  the  older  specifications.  What  the 
purchaser  really  wants  in  a  grain  elevator  is  a  belt  that  will  last  many  years 
without  separation  of  the  plies;  it  is  not  possible  to  get  this  by  a  specifica- 
tion that  merely  calls  for  so  many  pounds  friction  test,  because  a  high 
friction  test  does  not  necessarily  mean  a  rubber  that  will  last  a  long  time 
before  it  loses  its  elasticity  and  tenacity  (see  p.  36). 

Rubber  belts  for  grain  elevators,  as  now  made,  are  generally  of  32-ounce 
duck,  5,  6  or  7  plies  thick  according  to  the  service.  For  most  cases  it  is 
safe  to  use  a  "  friction  surface  "  belt,  that  is,  one  which  has  only  the  thin 
layer  of  friction  rubber  on  the  outside  surface  (Fig.  40),  but  where  the  grain 
is  handled  wet,  as  in  oats  bleachers,  a  rubber  cover  -^  or  YG  inch  thick  all 
over  is  necessary.  In  the  past,  rubber-covered  belts  were  standard  for  all 
grain  elevator  legs,  but  since  the  work  is  dry  and  not  abrasive,  a  rubber 
cover  is  not  highly  essential.  Some  experienced  buyers  prefer  to  spend 
their  money  for  quality  of  friction  rather  than  for  rubber  covers  on  leg 
belts.  The  fact  is  that  rubber  belts  with  a  low-grade  friction  do  not  hold 
together  unless  they  have  the  protection  of  a  rubber  cover.  The  friction 
in  "  competition  "  belts  is  apt  to  have  a  high  percentage  of  mineral  matter, 
and  consequently  a  poor  bond  between  the  plies  of  duck;  with  these  belts, 
the  standard  rubber  cover,  which  is  ^  or  ^  inch  thick,  serves  a  useful 
purpose  in  keeping  out  atmospheric  moisture;  and  it  prolongs  their  life. 
In  belts  of  better  grade,  the  friction  is  compounded  to  maintain  its  elas- 
ticity for  a  long  time;  it  forms  a  good  bond  between  the  plies  of  duck  and 
does  not  need  the  protection  of  a  cover  in  the  ordinary  work  of  elevating 
grain. 

The  trade-marked  belts  made  for  grain  elevator  work  by  experienced 
manufacturers  are  not  usually  sold  on  the  maker's  specifications  as  to 
weight  of  duck  or  quality  of  friction,  but  it  is  understood  in  the  trade  that 
they  are  equal  to  or  better  than  Stewart's  specifications  (see  p.  37). 

On  the  use  of  frictions  that  test  still  higher,  see  page  38. 

Rubber  Belts  for  Other  Service. — Many  good  conveyor  belts  are  made 
from  28-ounce  duck,  but  elevator  belts  are  seldom  made  from  duck  lighter 
than  32  ounces.  A  standard  32-ounce  duck  may  have  in  the  warp  23  threads 
per  inch,  7  yarns  per  thread,  and  in  the  filler  13  threads  per  inch,  6  yarns 
per  thread.  Belts  for  heavy  service  may  have  34-ounce  or  36-ounce  duck; 
the  heaviest  belts  are  built  from  42-ounce  duck. 


WEAR  ON  ELEVATOR  BELTS  249 

As  has  been  stated  (p.  53),  the  weight  of  duck  is  not  in  itself  a  measure 
of  the  strength  or  worth  of  the  Ipelt;  those  qualities  depend  also  upon  the 
proportion  of  warp  and  filler  threads,  the  twist  of  the  threads,  and  the 
manner  in  which  the  plies~are  held  together  by  the  friction  compound.  The 
skill  and  knowledge  of  the  belt  manufacturer  in  combining  these  with  the 
proper  grade  of  friction  and  with  the  right  covers,  when  necessary,  determine 
the  value  of  a  belt  for  a  particular  service  and  its  ability  to  withstand,  to 
an  economical  degree,  all  those  strains,  shocks,  cuts,  punctures  and  other 
distresses  to  which  elevator  belts  are  liable. 

Friction-surface  belts  have  on  their  outer  surfaces,  only  that  thin  layer 
of  friction  rubber  which  is  calendered  or  pressed  into  the  duck  before  it  is 
assembled  and  cured.  They  can  be  used  economically  for  some  fine  dry 
materials  like  crushed  ores,  pulverized  dry  coal,  dry  chemicals,  etc.;  but 
where  the  material  is  damp,  as  coal  often  is  from  exposure  to  rain  or  snow, 
or  where  the  ore  is  wet,  as  from  jigging  or  as  handled  in  the  flotation  process 
of  ore  separation,  then  a  rubber-covered  belt  is  preferable  for  several 
reasons : 

1.  The  rubber  cover  keeps  moisture  from  penetrating  the  cotton  fabric. 

2.  It  forms  a  cushion  to  prevent  the  fine  particles  which  stick  to  the 
belt  and  pulleys  from  b'eing  pressed  into  the  fabric. 

3.  When  the  belt  slips  and  creeps  on  the  head  pulley  as  it  always  does 
(see  p.  276)  the  rubber  protects  the  fabric  from  being  worn  away  by  the 
grit  always  present  between  the  belt  and  the  pulley. 

Wear  on  Elevator  Belts  is  internal  and  external.  If  the  material  handled 
is  clean,  dry,  not  abrasive,  not  lumpy,  belts  may  fail  because  the  friction 
dries  out  and  the  plies  come  apart;  if  the  material  is  clean  and  wet,  the 
plies  separate  sooner  because  water  enters  through  the  bolt  holes  or  through 
cuts  and  cracks;  and  the  external  wear  is  also  a  factor  because  the  belt  is 
more  likely  to  slip  on  the  wet  pulleys.  If  the  material  is  sharp  and  cutting 
as  well  as  wet,  the  external  wear  is  more  rapid,  and  if  the  pieces  are  also 
hard  and  large,  internal  and  external  wear  are  both  more  serious  from  the 
cuts  and  punctures  which  the  belt  receives. 

Adding  Covers  to  Elevator  Belts  is  a  means  of  equalizing  the  external 
and  internal  wear;  it  produces  a  balanced  construction  which  prolongs 
the  life  of  the  belts.  In  that  respect  it  is  like  adding  covers  to  conveyor 
belts.  Rubber  belts  were  not  a  success  for  conveying  coarse  materials 
heavier  than  grain  until  Robins  made  them  with  rubber  covers.  Similarly, 
in  many  elevators  handling  ore,  and  especially  wet  ore,  the  cost  of  upkeep 
has  been  greatly  reduced  by  the  use  of  belts  with  rubber  covers  on  one  or 
both  sides.  In  other  words,  in  spite  of  the  greater  cost  of  belts  with  rubber 
covers,  the  cost  of  elevating  one  ton  of  material  has  been  reduced  and  less 
time  has  been  lost  in  shut-downs  for  repairs  and  replacements  of  belts. 

Rubber-covered  Belts. — The  ordinary  -5-5  or  -^Q  inch  of  rubber  which 
characterizes  the  cheapest  rubber-covered  belt  serves  its  purpose  when 
it  is  required  merely  to  keep  out  atmospheric  moisture,  when  the  material 
is  not  lumpy  or  abrasive  and  when  the  slip  of  the  belt  on  the  head  pulley  is 


250  BELTS  FOR  ELEVATORS 

comparatively  slight.  Where  conditions  are  bad  in  these  respects,  a  thicker 
cover  is  needed  to  make  a  balanced  construction.  On  the  pulley  side,  a 
rubber  cover  maintains  a  good  contact  with  the  head  pulley  in  spite  of  dirt 
and  grit;  if  the  work  is  dry,  it  increases  the  coefficient  of  belt  contact; 
if  the  work  is  wet,  the  coefficient  may  not  be  any  greater  than  between  a 
wet  pulley  rim  and  a  friction-surface  belt,  but  the  cover  certainly  acts  as  a 
protection  to  the  fabric  when  the  belt  creeps  and  slips.  A  cover  on  the 
pulley  side  acts  also  as  a  cushion  to  prevent  injury  to  the  fabric  from  hard 
pieces  jammed  between  the  belt  and  the  foot  pulley. 

It  also  forms  a  cushion  into  which  the  heads  of  the  bucket  bolts  can  sink 
without  tearing  the  fabric,  and  the  heads  are  not  so  likely  to  come  into 
contact  with  the  pulley  rim.  When  the  bolt  heads  project  beyond  the  belt 
surface  and  bear  against  an  iron  pulley  rim,  the  belt  is  apt  to  slip,  especially 
if  wet.  If  the  head  pulley  is  lagged,  the  lagging  may  be  cut  and  torn  by  the 
bucket  bolts.  Conversely,  the  cover  on  the  pulley  side  of  the  belt  protects 
the  fabric  from  being  cut  by  the  lagging  bolts  or  rivets  which  often  project 
when  the  lagging  wears  thin.  This  may  occur  from  the  natural  creep  of  the 
belt  even  though  the  belt  may  apparently  not  slip  (see  Fig.  250  and  p.  277). 


FIG.  238.— Lagging  Bolts  Worn  by  Slip  and  Creep  of  Elevator  Belt. 

Fig  238  shows  a  group  of  bolts  used  to  fasten  rubber  lagging  to  the  rim 
of  a  head  pulley.  The  bolt  heads  have  been  worn  away  by  the  slip  and 
creep  of  the  elevator  belt. 

A  rubber  cover  on  the  bucket  side  of  the  belt  helps  in  several  ways. 

1.  It  protects  the  fabric  from  wear  caused  by  direct  impact  of  material 
against  the  belt  in  the  boot  or  from  a  feed  chute. 

2.  It  resists  the  tendency  of  the  forward  edge  of  the  bucket  to  cut  the 
belt,  either  from  hanging  forward  on  the  down  run  or  from  the  action  of 
centrifugal  force  in  passing  around  the  wheels. 

3.  It  prevents  the  bits  of  material  which  catch  back  of  the  bucket  from 
being  forced  into  the  fabric. 

Figs.  41  and  42,  page  23,  show  two  8-ply  elevator  belts,  one  with  the 
ordinary  ^-inch  rubber  covers  on  each  side;  the  other  has  -^  inch  on  the 
pulley  side,  |  inch  on  the  bucket  side  and  a  protection  for  the  edge  made 
by  carrying  the  top  cover  around  to  the  under  side. 

Thickness  of  Rubber  Covers  on  elevator  belts  has  been  a  matter  of 
trial  and  investigation  for  several  years.  The  size  of  the  ore,  its  sharpness, 


EXAMPLES  OF  CURRENT  PRACTICE  251 

and  whether  it  is  wet  or  dry,  the  size  of  pulleys  used,  the  size  and  spacing  of 
buckets — all  these  are  factors  wtyioh  determine  the  best  proportion  of  belt 
plies  and  belt  covers  which  makes  a  balanced  construction  for  a  particular 
elevator.  These  factors  ^differ  in  various  plants,  and  therefore  the  belt 
specification  for  the  best  service  and  lowest  cost  of  handling  will  also  differ. 
Examples  of  Current  Practice  are  given  below: 

1.  An  elevator  67-foot  centers  for  cement  clinker,  size  1  inch  and  under, 
60  pounds  per  cubic  foot,  temperature  160°  F.     Steel  buckets  20  by  12  by  8 
inches  every  17  inches  on  the  belt.     Head  pulley  48  inches,  foot  pulley  36 
inches.     Belt  22  inch,  8-ply,  36-ounce  duck — the  manufacturer's  best  grade, 
cover  on  pulley  side  -^  inch,  cover  on  bucket  side  YQ  mcn-     Speed  400  feet 
per  minute  =32  r.p.m.  of  head    pulley.     Belt    joint   lapped    and    bolted. 
Belt  lasted  450  days,  working  twenty-four  hours  a  day.     Life  and  service 
considered  very  satisfactory. 

2.  An  elevator  57-foot  centers,  inclined  about  10°  for  lead  ore,  size 
f  inch,  wet,  100  pounds  per  cubic  foot.     Steel  buckets  14  by  7  by  5  £  inches 
every  22  inches.     Head  pulley  42  inches,  foot  pulley  30  inches.     Belt 
16-inch,  8-ply,  36-ounce  duck — the  manufacturer's  best  grade,  cover  on 
pulley  side  -^  inch,  on  other  side  YQ  mcn-     Speed  385  feet  per  minute  = 
35    r.p.m.    of    head  wheel.     Belt    fastened  with  Jackson  fastener.     Belt 
lasted  682  days,  elevated  455,000  tons;  cost  of  belt  per  ton  of  ore  .076  cent. 
This  is  a  very  good  record. 

3.  An  elevator  48  foot-centers,  inclined  about  15°,  for  rejections  from 
jigging  ore,  size  f  inch  and  under,  damp,  160  pounds  per  cubic  foot.     Steel 
buckets  22  by  7  by  7  inches,  spacing  not  stated.     Head  pulley  31  inches, 
foot  pulley  24  inches.     Belt  22-inch,  7-ply,  36-ounce  duck — the  manu- 
facturer's best  grade  but  not  rubber  covered   (friction  surface).     Speed 
520    feet    per  minute  =64  r.p.m.  of  head  wheel.     Belt  lasted    126  days; 
cost  per  ton  of  material  elevated  .14  cent.     This  was  better  than  the  record 
of  other  belts  used  in  this  elevator,  but  the  life  was  not  so  long  as  it  might 
have  been  had  the  belt  been  rubber-covered  and  run  at  a  slower  speed. 
Five  hundred  and  twenty  feet  per  minute  means  83  r.p.m.  of  the  24-inch 
foot  wheel;   entirely  too  fast  for  the  pick-up  of  such  material  (see  p.  212). 
The  pulleys  were  too  small  in  diameter  for  7-ply  belt  (see  Chapter  V). 

4.  An  elevator  55-foot  centers,  inclined  slightly,  for  wet  ore,  ^  inch  size, 
100  pounds  per  cubic  foot.     Steel  buckets  14  by  7  by  5  £  inches  spaced  18 
inches,  head  and  foot  pulleys  36  inches.     Belt  15-inch,  6-ply,  grade  not 
stated;    covers  both  sides  YS  inch,  belt  joint,  Jackson  fastener,  belt  speed 
470  feet  per   minute  =50  r.p.m.  of  head  pulley.     Belt   lasted   632  days, 
twenty-four  hours  per  day.     A  good  record;   belts  seldom  lasted  over  one 
year  in  this  elevator.     Speed  is  too  high  for  a  36-inch  head  wheel. 

5.  An  elevator  58-foot  centers,  inclined  about  10°,  for  wet  ore,  size  f  inch, 
100  pounds  per  cubic  foot,  steel  buckets  14  by  7  by  5  £  inches  every  18  inches, 
head  and  foot  pulleys  36  inches.     Belt  15-inch,  7-ply,  36-ounce  duck — the 
manufacturer's  best  grade,   rubber-covered,  thickness  not  stated,   speed 
470  feet  per    minute  =50   r.p.m.  of   head    pulley.     Belt  lasted  416  days, 


252  BELTS  FOR  ELEVATORS 

handled  436,000  tons;  belt  cost  per  ton  elevated  .08  cent.  Considered  a 
good  record;  the  user  expects  belts  to  last  ten  or  twelve  months  on  this 
elevator.  Speed  is  too  high  for  a  36-inch  head  wheel. 

6.  An  elevator  65-foot  centers,  inclined  about  25°,  for  crushed  stone, 
size  3  to  8  inches,  dry,  100  pounds  per  cubic  foot.  Buckets  34  by  16  by  14 
inches  continuous  on  belt.  Head  pulley  48  inches,  foot  pulley  48  inches. 
Speed  250  feet  per  minute  =20  r.p.m.  of  head  wheel.1  Belt  38-inch  10-ply, 
36-ounce  duck — the  manufacturer's  best  grade  friction-surface  belt,  no 
rubber  covers.  Lasted  four  years  eight  months  and  carried  between 
1,500,000  and  2,000,000  tons  of  stone.  An  excellent  record,  the  best  ever 
made  on  that  elevator. 

Choice  of  Elevator  Belts. — The  kind  of  belt  best  suited  to  a  particular 
elevator  can  be  guessed  at  by  some  knowledge  of  what  has  given  good  service 
under  similar  conditions  elsewhere;  but  since  operating  conditions  are 
never  exactly  alike,  the  question  can  be  settled  in  a  purchaser's  mind  only 
by  trial.  The  true  test  of  an  elevator  belt  is,  "  What  does  it  cost  per  year 
or  per  ton  of  material  elevated  "?  There  are  places  where  a  belt  is  always 
discarded  on  account  of  external  injuries,  which  cannot  be  avoided  without 
serious  changes  in  methods  or  equipment  and  at  too  great  expense,  and  in 
which  the  wear  cannot  be  resisted  by  any  degree  of  high  quality  in  the 
friction,  or  duck,  or  cover  of  the  belt.  In  such  cases,  to  buy  expensive  belts 
is  throwing  money  away.  On  this  subject,  see  Chapter  III. 

In  normal  elevators,  however,  the  ordinary  causes  of  belt  failure  are  well 
known,  and  they  can  be  opposed  successfully  by  using  the  right  kind  of 
duck  or  the  proper  kind  of  friction  or  covers  suited  to  the  work.  The  main 
thing  is  to  have  the  belt  so  strong  that  it  will  not  fail  suddenly  under  an 
accidental  overload,  or  a  choke  from  buckets  ripping  off,  or  a  stick  falling 
into  the  boot,  etc.  A  sudden  shut-down  through  the  breakage  of  a  belt  may 
cost  more  in  lost  output  of  product,  and  in  emergency  repairs,  than  the  price 
of  a  good  belt.  When  the  right  belt  has  been  chosen,  it  should  be  inspected 
regularly,  and  it  will  give  plenty  of  notice  before  it  is  worn  out;  then  a  new 
belt  can  be  ordered  at  the  proper  time  in  advance  and  when  the  day  comes 
to  put  it  in  place,  the  replacement  can  be  made  in  an  orderly  routine  way 
without  interruption  of  service  and  at  the  least  cost. 

On  the  relation  between  bucket  width  and  belt  width,  see  p.  261. 

On  the  relation  between  belt  tension  and  belt  thickness,  see  p.  274. 

Wet  Elevating. — Handling  the  semi-liquid  pulps  in  the  wet  concentra- 
tion of  ores  is  hard  work  for  belts.  Ordinary  belts  do  not  last  long;  the 
coefficient  of  belt  contact  with  wet  surfaces,  rubber  to  rubber  or  rubber  to 
iron,  is  only  about  half  that  of  a  dry  belt  on  a  lagged  pulley;  the  belt  is 
apt  to  slip  unless  it  is  pulled  tight,  and  that  slip  in  the  presence  of  the  fine 
grit  which  sticks  to  belt  and  pulleys  wears  out  the  driving  face  of  the 
belt.  The  fine  sand  in  the  pulp  works  into  the  fabric  through  cuts  and 
cracks,  the  plies  separate  and  sand-blisters  form.  The  water,  getting  into 
the  cotton,  mildews  it,  and  the  plies  come  apart.  For  these  reasons  a 
iThis  is  not  a  centrifugal  discharge  elevator. 


COVERS  FOR  WET  ELEVATOR  BELTS 


253 


friction-surface  belt  is  out  of  place  in  handling  mineral  pulps,  and  even  an 
ordinary  rubber-covered  belt  with  its  -^  or  ^V  inch  of  cover  does  not  usually 
return  good  service  for  the  mone^  spent  on  it,  because  the  thin  rubber  is 
soon  rubbed  off  by  the  sfip  and  creep  of  the  belt  combined  with  the  gritty 
sand. 

Covers  for  Wet  Elevator  Belts. — Experiments  made  by  mining  com- 
panies for  several  years  past  have  demonstrated  the  value  of  comparatively 
thick  covers  on  the  pulley  side  of  belts  handling  wet  ores  and  mineral 
pulps.  One  copper  company  uses  belts  with  -^-inch  cover  on  the  pulley 
side  and  ^-inch  on  the  bucket  side;  another  company  uses  covers  ^--inch 
and  ^-inch  on  pulley  side  and  bucket  side,  respectively;  a  lead-mining 
company  uses  ^-inch  rubber  on  the  pulley  side  and  only  y^-inch  on  the 


FIG.  239. — Elevator  Belts  with  Rubber  Covers  on  Both  Sides.     Covers  Cemented  and 
Vulcanized  with  Tie-gum  Construction.     (B.  F.  Goodrich  Rubber  Co.) 

other  side,  depending  on  flaps  of  old  belt  (see  Fig.  242),  bolted  under  the 
buckets  to  protect  the  belt  from  cutting  and  abrasion. 

Fig.  239  shows  cross-sections  of  elevator  belts  made  especially  for 
handling  wet  pulps  (B.  F.  Goodrich  Rubber  Co.).  The  8-ply  belt  has 
f-inch  covers  on  each  side  and  the  6-ply  belt  has  A-inch  covers.  The 
layers  of  friction  rubber  rolled  into  the  duck  are  thicker  than  usual,  so  as 
to  make  the  belt  quite  flexible  in  spite  of  its  thickness  and  to  keep  water 
out  of  the  fabric  if  the  belt  should  be  cut  or  the  covers  worn  away.  The 
covers  are  cemented  to  the  body  of  the  belt  with  the  "  tie-gum  "  con- 
struction referred  to  on  page  25. 

Width  of  Belts. — Belts  for  wet  elevators  should  be  wider  than  for  dry 
elevating.  There  are  several  reasons  for  this: 

1.  The  water,  over  and  above  what  fills  the  voids  in  the  crushed  ore, 
must  be  provided  for  in  choosing  the  size  of  the  buckets,  and  hence  the  width 
of  the  belt. 


254 


BELTS  FOR  ELEVATORS 


2.  Thin  pulps  are  apt  to  splash  out  of  the  buckets  in  the  pick-up  and 
be  forced  out  over  the  lip  of  the  bucket  by  the  resultant  of  the  forces  due  to 
centrifugal  force  and  gravity  (see  p.  220).      Hence  it  is  safe  to  use  only  a 
fraction  of  the  nominal  capacity  of  the  buckets,  as  given  in  manufacturers' 
catalogues.     Some  experienced  millmen  use  only  one-third  of  the  nominal 
capacity. 

3.  As  between  a  narrow  belt  with  buckets  that  project  far  from  the 
belt,  or  a  wide  belt  with  buckets  of  less  projection,  the  wide  belt  is  preferable; 
it  is  less  likely  to  slip  on  the  wet  pulley,  and  the  pressures  which  tend  to 
cut  or  wear  the  belt  are  less  per  square  inch  of  belt  surface. 

See  page  221  on  the  pick-up  and  discharge  of  mineral  pulps. 

Belts  for  Continuous  Bucket  Elevators. — The  steel-plate  buckets  used 
in  these  elevators  weigh  more  per  foot  of  belt  than  buckets  used  in  centrif- 
ugal discharge  elevators;  the  backs  are  always  flat,  the  projection  generally 


FIG.  240.— Elevator  Belts  with  Heavy  Duck  for  Hard  Service. 

Rubber  Co.) 


(B.  F.  Goodrich 


greater  than  with  round-bottomed  buckets,  and  the  distance  A  (Fig.  264) 
relatively  smaller  compared  with  the  dimensions  of  the  bucket.  Con- 
sequently the  pull  on  the  bolts  is  severe,  and  unless  the  belt  is  stiff  and  strong 
it  may  be  injured  on  the  pulley  side  by;  the  pressure  of  the  heads  of  the 
bucket  bolts;  or  the  bolts  may  pull  clear  through  the  belt. 

For  these  reasons,  and  because  of  the  great  wear  on  the  belt  surface, 
belts  for  heavy  continuous  bucket  elevators  should  be  made  of  duck  heavier 
than  the  32-ounce  used  in  most  rubber  belts  for  elevator  service.  Rubber 
belts  with  36-ounce  and  42-ounce  duck  are  made  for  heavy  stone  and  ore 
elevators  with  continuous  buckets,  generally  with  thin  rubber  covers  for  dry 
work.  Fig.  240  shows  two  specimens;  the  6-ply  belt  has  warp  threads 
larger  and  fewer  per  inch  than  in  ordinary  elevator  belts,  and  the  filler 
threads  are  correspondingly  closer  and  thicker.  The  8-ply  belt  shows  a 
very  heavy  close-woven  duck. 

Stitched  canvas  belts  made  of  standard  32-ounce  duck — 37-ounce  on 
the  basis  on  which  rubber  belts  are  graded  (see  p.  46) — show  great  resist- 


BELTS  FOR  CONTINUOUS  BUCKET  ELEVATORS  255 

ance  to  the  tendency  of  the  bolts  to  pull  through  the  belt,  especially  when 
saturated  with  a  Class  1  dryirfg  compound  (see  p.  47)  and  properly 
stretched  and  cured.  For  strength^  canvas  belts  see  Chapter  III. 

Balata  belts  made  of  38-ounce  duck  have  a  density  and  strength 
which  fits  them  for  work  of  this  kind.  For  strength  of  balata  belts  see 
Chapter  III. 


CHAPTER  XIX 
FASTENING  BUCKETS  TO  BELT 

Fastening  Buckets  to  Belt. — Since  a  belt,  in  passing  around  a  pulley, 
forms  an  arc  tangent  to  the  flat  back  of  a  bucket,'the  bolts  which  fasten  on  the 
bucket  should  theoretically  be  in  a  single  row  across  the  back  of  the  bucket. 
This  is  the  rule  on  all  elevators  handling  grain  and  similar  materials:  the 
bodies  of  grain  buckets  are  made  of  tin  plate  or  light  sheet  steel,  No.  24  or 
No.  26  gauge,  and  the  holes  are  punched  in  a  single  row  through  the  fold  of 
metal  or  reinforcing  band  at  the  top  of  the  back.  If  the  entire  back  were 
thick,  as  in  malleable-iron  buckets  or  in  seamless  steel  buckets,  it  would  be 
possible  to  get  a  better  grip  on  the  belt  by  using  bolts  in  two  rows  an  inch 
or  two  apart,  but  unless  the  pulleys  are  relatively  large,  or  the  rows  close 
together,  this  practice  will  injure  the  belt  or  the  bucket. 

From  Fig.  241,  representing  a  belt  on  a  pulley,  it  is  evident  that  if  the 
holes  are  punched  in  the  bucket  for  two  rows  of  bolts,  and  if  the  belt  while 
legforl}otg  straightened   out  is   punched   to  match,   the 

holes  no  longer  match  when  the  belt  runs  over 
a  pulley;  the  holes  in  the  belt  are  pulled  out 
of  parallel  by  the  bend  of  the  belt  and  a  gap 
opens  between  the  belt  and  the  back  of  the 
bucket.     The  difference  between  the  chord  A 
and  the  arc  B  is  not  great  (see  Table  47),  but 
FIG.  241. —Double  Row  of  Bucket  for  a  7-  or  8-ply  belt  which  is  £  inch  thick,  the 
Bolts    Passing    Over    Pulley.    difference   of   the  arcg  B  and  C  is  more  than 
(See  Table  48.)  .  .  . 

•jV  inch  for   a   row   spacing   of  2    inches  on 

pulleys  of  34-inch  diameter  or  less.  Bolt  holes  in  buckets  are  made  rg- 
inch  larger  than  the  bolts  and  allow  some  freedom  for  the  bolts;  but  too 
much  movement  of  that  kind  is  apt  to  cut  off  the  bolts  or  wear  out  the 
backs  of  the  buckets  where  the  nuts  bear  against  them. 

The  gap  D  is  jfe  inch  or  more  for  a  row  spacing  of  2  inches  in  a  belt  as  it 
bends  over  a  pulley  of  34-inch  diameter  or  less.  This  dimension  is  a  measure 
of  the  tendency  of  the  bolts  to  bend  the  backs  of  the  buckets  or  pull  through 
the  belt  when  passing  over  a  pulley.  There  is  a  definite  pull  on  these  bolts 
when  the  bucket  digs  its  load  out  of  a  boot,  and  when  the  material  is  hard 
and  lumpy  and  the  belt  speed  high  it  is  not  uncommon  to  find  the  belt  on 
the  pulley  side  injured  by  the  movement  of  the  bolts;  or  the  bolts  may  even 
pull  clear  through  the  belt. 

Continuous  Buckets  on  Belt. — The  large  steel-plate  buckets  used  on 
stone  elevators  are  often  so  heavy  that  it  is  necessary  to  fasten  them  to 

256 


MALLEABLE-IRON  BUCKETS  ON  BELTS 


257 


TABLE  47.— DIMENSIONS  OF  FIG.  241  FOR  TWO  ROWS  OF  BOLTS 
2  INpHES  APART 


Diameter  of  Pulley. 

Arc  B—  Chord  A 

Arc  C  —  Arc  B 

Gap-D 

For  Belt  \  Inch  Thick. 

Inches 

Inches  * 

Inches  f 

Inches  * 

12 

.010 

.167 

.091 

24 

.0025 

.083 

.044 

36 

.001 

.056 

.030 

48 

.0004 

.042 

.022 

96 

.0002 

.021 

.010 

*  Proportional  for  spacings  other  than  2  inches  (approximately). 
t  Proportional  for  thicknesses  other  than  |  inch. 

the  belt  by  two  rows  of  bolts  to  prevent  them  from  pulling  loose  or  injuring 
the  belt.  These  rows  are  midway  in  the  height  of  the  back  of  the  bucket; 
whether  they  are  1  or  2  inches  apart,  the  head  and  foot  pulleys  should  not 
be  less  than  30  inches  in  diameter,  and  the  loading  should  be  arranged  so 
that  the  buckets  receive  material  direct  from  a  chute  while  on  a  straight 
run  and  never  have  to  dig  out  of  a  boot  or  even  come  into  contact  with 
material  spilled  under  the  foot  wheel. 

Malleable-iron  Buckets  on  Belts. — In  belt  elevators  handling  ores  and 
other  gritty  and  heavy  materials  it  is  customary  to  use  malleable-iron 
buckets;  and  when  the  projection  of  the  lip  from  the  belt  exceeds  5  or  6 
inches  the  pull  on  the  bolts  from  the  digging  and  from  the  weight  of  the 
bucket  is  often  too  much  for  a  single 
row  of  bolts.  In  spite  of  the  disad- 
vantages of  two  rows  of  bolts,  it  is 
advisable  to  use  two  rows  for  buckets 
10  by  6  inches  and  larger.  If  the 
rows  are  not  over  f  inch  apart,  the 
difference  between  B  and  C  (Fig.  241) 
is  less  than  -^j  inch  for  all  belts  not 
over  ^  inch  thick  on  pulleys  at  least 
24  inches  in  diameter,  and  D  is  less 
than  ^j  inch  under  the  same  condi- 
tions. For  spacing  of  bolts  see  Table 
49. 

At  any  rate  it  is  better  to  hold  the 
buckets  on  securely  and  avoid  acci- 
dent, even  though  the  wear  on  the 
belt  may  be  somewhat  greater.  It 
may  be  said,  however,  that  the  ten- 
dency to  cut  the  belt  at  A  (Fig.  242) 
may  be  less  when  the  bucket  is  held 
by  two  rows  of  bolts.  This  is  par- 
ticularly true  on  the  down  run  of  belt;  heavy  buckets  upside  down  tend 


FIG.  242. — Devices  to  Protect  Elevator 
Belts  from  Injury  where  Buckets  are 
Bolted  on. 


258  FASTENING  BUCKETS  TO  BELT 

to  swing  away  from  the  belt  with  the  leading  edge  as  &  pivot  (see  G,  Fig. 
242).  Some  bits  of  material  are  always  picked  up  in  the  boot  where  the 
bucket  gaps  away  from  the  belt  and  carried  between  the  belt  and  the 
back  of  the  buckets  ahead  of  the  bolts.  Any  pressure  there  when  the 
bucket  is  inverted  may  force  particles  into  the  belt  and  damage  it,  unless 
a  pad  of  belting  (see  C,  Fig.  242)  is  used  back  of  the  bucket  or  unless  the 
bolts  are  kept  tight. 

Besides  bolts,  other  methods  have  been  used  or  proposed  to  fasten 
buckets  to  belts.  Oliver  Evans  (see  p.  247)  used  straps  and  buckles; 
Griscom,  in  1896,  patented  a  sheet-metal  clip  fastened  to  the  bucket  and 
bent  over  the  edges  of  the  belt.  Another  inventor  proposed,  in  1914,  to 
fold  the  belt  into  a  loop  at  each  bucket  and  fasten  the  bucket  to  the  loop. 
Filling  and  discharge  of  the  bucket  were  apparently  secondary  items  in  this 
design.  None  of  these  schemes  is  in  use  at  present;  others  could  be 
mentioned,  but  they  are  not  so  cheap,  simple  and  handy  as  the  bolt 
fastening. 

Pull  on  Bolts. — When  a  bucket  with  a  flat  back  is  fastened  to  a  belt 
by  a  single  row  of  bolts  there  is  only  a  short  contact  between  it  and  the  belt 
as  it  bends  around  a  pulley.  When  the  strain  of  digging  comes  on  a  bucket 

7?  P 

there  is  a  pull  on  the  bolts  which  in  Fig.  243  is  measured  by  T  = ,  where 

A. 

R  is  the  resistance  to  the  travel  of  the  bucket  through  the  boot.  The 
value  of  T  for  a  given  bucket  can  be  reduced  by  making  the  bucket  with  a 

ffP 

curved  back  as  in  the  Buffalo  bucket  (Fig.  219);   then,  in  Fig.  243,  T  = . 

B 

Since  B  may  be  two  or  three  times  A,  the  pull  on  the  bolts  is  only  one-half 
or  one-third  as  much  and  where  the  digging  is 
severe,  as  in  grain  elevator  boots  filled  up  above  the 
level  of  the  foot  shaft,  or  at  the  foot  of  marine  legs 
(Fig.  263)  digging  cargo  grain,  it  is  advisable  to  use 
buckets  with  the  curved  back. 

To    some   extent,    the    same    may   be    said    of 
buckets   fastened   on   by  two  rows  of  bolts.     The 
bucket  then  has  a  longer  contact  with  the  belt  and 
Fm.   243. -Pull    on     the  pull  on  the  bolts  is  less. 

Bucket  Bolts  De-  The  elevator  bucket  shown  in  Fig.  232  is  used 

pendent  on  Shape  of     on  grain  elevators  in    Europe ;    it  has  a  flat  back, 

but  the  sheet  forming  the  bottom  is  extended  and 

flanged  at  the  lower  end  to  act  as  a  prop  against  the  belt  in  going  around  the 
foot  wheel.  With  this  construction,  the  distance  corresponding  to  A  or  B 
(Fig.  243)  is  even  greater  than  in  the  Buffalo  bucket,  and  the  pull  on  the 
bolts  is  therefore  less.  At  the  same  time,  in  going  over  the  head  wheel,  the 
extended  bottom  sheet  acts  as  a  deflector  for  the  discharge  from  the  following 
bucket,  and  the  buckets  therefore  can  be  placed  close  together  or  slightly 
overlapping. 

Tables  48  and  49  (Weller  Manufacturing  Co.)  give  standard  sizes  and 


SPACING  OF  BUCKET  BOLTS 


259 


I 

a 
-1 

30 

-il 

1  Number 
of  Bolts 

1 

J 

"3 

I 

8 

1 

-is 

-3 
3 

r 

1 

1 

i 

i 

I 

v 

t 

* 

fOcoTjoococococococococococococococococorococococo  co  co  co  co  co 

iii 

1  Number 
of  Bolts 

i 

f 
I 

^  i 

T" 

i 

a 

<4 

£ 

H 
Pi 

c 

p 

^ 

c 

2 

^ 

t 
a 

a 

«< 

i 

'  < 
& 

BUCKET  PUNCHING.  (For  Attaching  iLJ  t  V  *W  V  ij  /f  VW*W*UW 
Buckets  to  Belts)  V  /  V  /I  J 

- 

^^cocococo^^^^^^^^coco 

H 

I 

f 

.Q 

.-if 

oc 

I 

a 

9 

w 

PQ 

Il 

•tttt&BttW^ 

p 

H 

:::::::::::::::::::  :  ,HN,^HC,nw,BH,        :::::::: 

...................    .cscs^^^coco    ........ 

Q 

;  :  n  :  ;  i.n  MI  ni  n  N  ;««««w^?  M  M  M  1  1 

ffl 

*«h*          1       1       1    H«    1       1                    III 

•< 

•  ^H  r-t  <N  (N  CO  CO  rt<  1C  CO  CO  •<*  (N  CO  CO  CO  CO  'ttCGtF      •                 ...      .  oo'po'co  CO  •*  ^  r^rr 

0 

Bolt  Holes 

II 

*<^W^WH>Wt*H^*** 

p 

Favorite,  Buffalo,  Ris 

s 

m-»nw             ......'.. 

(MINCOCO           

q 

*«*• 

co  co  co  co        

w 

HSHS^   .»,.•*  w     ,  HS  , 

^ 

,.  ,  «.  „„,.  ,««,„  •«     -i«  -N.     HS-P.^     -N-M  :  :  :  :W^H--G 

1 

0 

"S 

o 
3 

« 
"8 

1 

!  liiii  !  !  ! 

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 

260 


FASTENING  BUCKETS  TO  BELT 
TABLE  49.— MALLEABLE  BUCKETS 


k-*^*-)    .,      u,^.^^    *      L^J^i^i    { 

ll  i  I  t  l/iidT-h-hrl^aiihhld-ff 

r~ra_/^| 


Number  of  Holes  .  .  . 

2  Holes 

3  Holes 

5  Holes 

7  Holes 

9  Holes 

Width  of  Bucket  .  .  . 

4 

5 

6 

7 

8 

9 

10 

11 

12 

14 

16 

18 

20 

A  

3 
1 

3 
1 

2 
1 

2£ 

1 

3 

1 

3| 

1 

3^ 
1 
! 

3f 
1 

3 

4 

41 
1 
i 

4 

3* 
1 

i 

4 
1 

3 

4 

3£ 
1 
t 

4 
1 

3 

4 

B  

c 

Bolt  holes  in  malleable  buckets  all  ^-inch  diameter  for  |-inch  bolts. 

spacing  of  holes  in  sheet-steel  and  malleable-iron  buckets  for  attaching  to 
belts. 

Damage  to  Belts  where  Buckets  Are  Bolted  On. — Heavy  steel  or  mallea- 
ble-iron buckets  fastened  to  belts  and  used  to  elevate  hard,  sharp  ores,  coke 
and  minerals,  often  cut  the  belt  at  A  (Fig.  242),  especially  if  the  bolts  get 
loose  and  allow  the  bucket  to  move  with  relation  to  the  belt.  Bolts  loosen 
from  several  causes: 

1.  Nuts  slacking  off. 

2.  Metal  of  the  bucket  wearing  away  under  the  nuts. 

3.  Belt  wearing  thin,  or  back  of  bucket  wearing  thin,  from  moving  on 
each  other. 

4.  Bolt  heads  wearing  deep  into  the  belt. 

When  the  bolts  get  loose,  centrifugal  action  at  the  pulleys  tends  to 
throw  the  bucket  outward  with  the  leading  edge  of  the  back  as  a  fulcrum, 
and  the  pressure  there  drives  hard  particles  into  the  belt;  or  the  edge,  if 
sharp,  may  cut  the  belt. 

There  is  generally  some  wear  between  the  belt  and  the  flat  back  of  the 
buckets  used  in  elevating  hard,  gritty  materials.  Some  of  the  discharge 
gets  into  the  gap  which  opens  there  in  going  over  the  head  wheel,  or  dribbles 
into  it  when  the  buckets  are  inverted  on  the  descending  run  and  hang  away 
from  the  belt  (G,  Fig  242).  The  same  thing  happens  at  the  foot  wheel 
when  the  buckets  gap  away  from  the  belt. 

Protective  Devices. — Various  devices  are  in  use  to  protect  the  belt  from 
the  wear  mentioned  above.  A  rubber  cover  on  the  belt  is  often  the  cure 
and  may  pay  for  itself  in  the  longer  life  of  the  belt  and  the  lower  cost  of 
repairs  and  renewals.  In  one  elevator  where  the  life  of  the  belts  averaged 
only  a  few  months,  triangular  prisms  of  wood  (B,  Fig  242),  equal  in  length 
to  the  width  of  the  belt,  were  fastened  on  by  wood  screws  below  each 
bucket  to  prevent  small  bits  from  getting  between  the  belt  and  the  bucket. 
This  scheme  cost  only  a  few  dollars,  but  it  more  than  doubled  the  life  of  the 
belt. 

In  the  Western  mining  country  where  centrifugal  discharge  belt  ele- 


TROUBLES  FROM  BUCKETS  WORKING  LOOSE  261 

vators  are  extensively  used  for  handling  not  only  fine  material,  wet  or  dry, 
but  also  lump  ore  up  to  3-inch  size,  it  is  common  practice  to  use  a  pad  of 
old  belt  between  the  bucket  and'Hhe  elevator  belt  (C,  Fig.  242).  Some- 
times the  bucket  bolts  do  not  go  through  the  elevator  belt,  but  only  through 
the  pad,  which  is  then  extended  above  and  below  each  bucket  to  protect 
the  belt  from  abrasion  (D,  Fig.  242).  This  is  open  to  the  objection  that 
unless  the  bolts  are  kept  tight,  fine  stuff  will  work  in  between  the  pad 
and  the  belt  and,  being  confined  there,  will  rub  and  injure  the  belt. 

In  wet  elevators  a  narrow  strip  of  old  belt  is  used  with  each  bucket  bolt 
(E,  Fig.  242)  to  space  the  bucket  away  from  the  belt  and  leave  room  for 
water  to  wash  away  the  grit  from  behind  the  bucket.  Soft  rubber  washers 
(F,  Fig.  242)  have  been  used  for  the  same  purpose  and  to  keep  the  leading 
edge  of  the  back  from  digging  into  the  belt.  Buckets  mounted  on  thick 
washers  cannot  do  heavy  digging  in  a  boot. 

Troubles  from  Buckets  Working  Loose. — Besides  the  cutting  of  the  belt 
mentioned  above,  there  are  other  troubles,  still  more  serious,  due  to  nuts 
working  loose  and  coming  off  the  bolts.  When  only  a  few  bolts  in  a  bucket 
stay  tight,  the  strain  on  them  is  excessive  and  they  may  damage  the  pulley 
side  of  the  belt  or  pull  through  the  belt,  or  break  off.  A  bucket  falling  off 
into  the  boot  may  rip  other  buckets  off  and  cause  a  breakdown;  buckets 
thrown  off  into  the  head  chute  may  damage  machinery  fed  by  the  elevator, 
or  cause  spouts  and  hopper  gates  to  choke.  In  grain  elevators  it  is  good 
practice  to  put  a  grating  near  the  top  of  the  head  chute  to  catch  such 
loose  buckets,  as  well  as  the  sticks  of  wood,  pieces  of  paper,  etc.,  which 
often  pass  from  grain  cars  into  the  elevator  leg.  A  clean-out  door  should 
be  provided  to  give  access  to  the  screen  for  examination  and  cleaning  (see 
Fig.  290). 

Inspection  of  Buckets. — Trouble  and  expense  can  be  avoided  by  inspect- 
ing buckets  and  their  fastenings  regularly  and  tightening  or  replacing  the 
loose  or  broken  bolts.  If  the  belt  shows  signs  of  being  cut  or  worn  by  the 
buckets  or  bolts  new  spots  can  be  made  to  take  the  wear  by  shifting  all  the 
buckets  to  new  positions  somewhere  between  the  old  positions.  Some  men 
who  install  belt  elevators  punch  the  belt  at  the  start  for  two  or  three  settings 
of  buckets;  that  is,  if  the  buckets  are  to  be  spaced  18  inches  apart,  the  new 
belt  would  be  punched  for  bolts  every  9  or  6  inches.  This  saves  time  and 
money  when  it  becomes  necessary  to  shift  the  buckets. 

Width  of  Bucket  and  Width  of  Belt. — The  usual  crown  of  belt  pulleys 
is  |  inch  on  the  diameter  per  foot  of  face — that  is,  the  face  of  a  pulley  for  a 
12-inch  belt  is  3^  inch  higher  in  the  center  than  at  the  edges.  When  a  belt 
runs  over  a  crown-face  pulley  its  center  is  stretched  more  than  its  edges, 
and  a  bucket  fastened  to  the  belt  must  either  bend  in  the  back  or  tend  to 
pull  the  bolts  through  the  belt;  or  else  the  belt  does  not  conform  exactly 
to  the  crown  along  the  line  of  the  bolts.  In  grain  elevators  the  belts  are 
relatively  stiff  and  the  buckets  light  and  the  back  of  the  bucket  springs 
slightly  to  match  the  crown  when  the  face  is  not  too  wide.  Sheet-steel 
buckets  of  heavier  metal  do  not  spring  so  easily,  and  malleable-iron  buckets 


262 


FASTENING  BUCKETS  TO  BELT 


are  too  stiff  to  spring  at  all.  Hence  it  happens  that  when  wide  stiff  buckets 
are  fastened  to  a  belt  of  the  same  width  the  bolts  are  apt  to  dig  into  and 
injure  the  pulley  side  of  the  belt.  Instead  of  using  malleable-iron  or  stiff 
steel  buckets,  say,  20  inches  or  wider  on  a  belt  of  that  width,  it  is  better  to 
use  smaller  buckets  of  half  the  width  in  double  row  to  give  the  required 
capacity.  The  spacing  between  consecutive  buckets  in  each  row  should, 
of  course,  be  what  will  give  a  clean  discharge  at  the  head,  and  if  the  widths 
of  the  buckets  in  the  two  rows  do  not  overlap  along  the  center  line  of  the 
belt  there  will  be  no  interference  with  the  discharge  when  the  buckets 
are  set  staggered. 

Buckets  in  Double  Row. — In  grain  elevators  and  other  elevators  using 
wide  belts  it  is  now  general  practice  to  use  double  rows  of  staggered  buckets 

when  belts  are  wider  than  22  inches  (see 
Fig.  244).  The  advantages  of  this  construc- 
tion are  as  follows:  (1)  The  buckets  avoid 
the  crown  of  the  pulleys.  (2)  The  buckets 
are  stronger  and  stiffer  and  the  fronts  are 
less  likely  to  pull  out  under  heavy  load,  or 
on  striking  an  obstacle  like  a  stick  of  wood 
in  the  boot.  (3)  If  a  bucket  is  spoiled  by 
any  mishap,  the  cost  of  replacing  it  is  less 
than  if  the  accident  happened  to  a  bucket 
of  double  the  width.  (4)  The  work  of  pull- 
ing the  buckets  through  a  deep  mass  of 
material  in  the  boot  is  less  than  for  wide 
buckets  in  single  row. 

Belts  in  Casings. — When  elevator  belts 
run  in  casings  it  is  usual  to  make  the  width 
of  the  belt  2  inches  more  than  the  width  of 
the  bucket,  or  1  inch  more  if  the  bucket  is 
FIG.  244.— 15-inch  Buckets  Spaced   not  Over  6  inches  wide;  then  there  is  a  mar- 
13   Inches   in   Double   Row  on       .         fit,  -i       •  -i         i  •  i     i  .1 

32-inch  Belt  Sm   °^  kelt    on    eac^    S1(*e  wmcn    keeps    the 

bucket  from  striking  the  casing.     Of  course 

casings  are  supposed  to  be  made  with  clearance  enough  to  avoid  inter- 
ference, but  if  they  should  twist  or  get  out  of  line,  it  is  better  that  the  belt 
should  rub  than  that  the  bucket  should  strike. 

If  there  is  no  casing,  or  if  the  elevator  is  enclosed  in  a  roomy  housing, 
the  margin  of  belt  is  not  necessary  as  a  guard;  but  where  the  head  pulley 
gets  wet  or  works  in  a  cloud  of  dust,  a  belt  no  wider  than  the  buckets  is 
more  likely  to  slip  than  a  belt  made  a  few  inches  wider.  The  coefficient  of 
belt  contact  is  less  under  such  circumstances  than  when  the  head  pulley 
is  dry  and  free  from  dust. 

Buckets  to  Match  Crown  of  Pulleys. — A  patent  was  granted  in  1916 
(No.  1194308)  on  a  bucket  with  its  back  curved  to  match  the  crown  of  the 
pulley.  Such  buckets  are  not  in  practical  use.  The  idea  might  be  applied, 
with  some  advantage,  to  wide  buckets,  but,  for  reasons  stated  above,  it 


JOINING  ENDS  OF  ELEVATOR  BELTS 


263 


is  better  to  use  narrower  buckets  in  two  rows  instead  of  very  wide  buckets 
in  single  row.  Aside  from  that,,  there  are  mechanical  difficulties  in  making 
sheet-steel  buckets  with  the  curve  for  crowning  combined  with  the  curve 
in  the  bottom  of  the  bucket.  It  would  be  still  more  difficult  to  apply  the 
idea  to  grain  buckets  with  a  curved  back  like  Fig.  219.  but  malleable-iron 
buckets  could  be  made  with  that  feature  if  there  were  a  demand  for  it. 

Joining  Ends  of  Elevator  Belts.  —  The  requirements  for  a  good  joint 
for  elevator  belts  differ  in  some  ways  from  those  for  conveyor  belts.  In 
the  latter,  the  fastening  must  be  flat  on  both  sides  because  both  sides  of  the 
belt  run  over  the  idlers.  In  elevator  belts,  the  fastening  need  not  be 
flush  or  even  flat  on  the  bucket  side  of  the  belt;  the  pull  in  the  belt  per 
inch  per  ply  is  often  greater  than  in  conveyor  belts  and  a  stronger  splice 
is  needed.  Another  difference  is  that  the  take-up  in  an  elevator  is  usually 
shorter  (see  p.  292),  resplicing  must  be  done  oftener,  and  a  fastening  that 
can  be  taken  apart  and  put  together  readily  in  a  confined  space  is  preferable. 
For  these  various  reasons,  elevator  belts  are  joined  with  bolted  splices 
rather  than  with  clinch  hooks  or  clinch  rivets. 

One  of  the  oldest  and  simplest  fastenings  is  shown  in  Fig.  245.     It  is 


x"\  ,„".„ 

K  W'BoHs3 

V—  \ 


3Pitch 


A 


FTG.  245.  —  Bolted  Clamp  Joint 
for  Elevator  Belt. 


^  Bolts  especially  at  Endi  o'  Lap  must  be  kept  Tight' 
Inda  of  Lacs  must  be  Cut  off  Cloie  to  Bolts '      ~"" 

FIG.  246.— Bolted  Lap  Joint. 


very  strong  and  resists  shocks,  but  it  is  not  easy  to  apply  to  belts  over 
5-ply,  and  when  it  is  put  on  thick  belts,  the  bending  in  going  over  pulleys 
is  localized  at  the  corners  of  the  flat  bars,  even  though  they  are  rounded. 
This  leads  to  breaking  the  warp  threads  and  to  cracking  the  belt  crosswise. 
This  joint  should  not  be  used  on  canvas  belts;  they  are  too  stiff  and  the 
duck  is  too  heavy  to  stand  the  bending. 

Lap  Joints.  —  The  joint  used  most  frequently  on  grain  elevator  belts 
and  for  heavy  continuous  bucket  elevators  is  a  plain  lap  splice  (Fig.  246). 
The  lap  may  cover  a  distance  of  4  feet  or  more  and  is  held  together  by  the 
bucket  bolts.  The  joint  is  simple  and  strong  and  requires  no  extra  parts; 
when  the  belt  becomes  too  long,  it  is  shortened  by  one  or  two  bucket  spacings, 
bolted  together  again,  and  the  excess  length  is  cut  off.  It  is  successfully 
used  on  5-  or  6-ply  grain  elevator  belts,  but  on  8-ply  belts,  the  double 
thickness  at  the  lap  measures  about  1  inch,  and  when  this  bends  over 
pulleys,  the  two  thicknesses  tend  to  move  on  each  other  and  there  are 
strains  which  work  the  bolts  loose  in  the  holes  and  cause  wear  on  the  belt 
under  the  bolt  heads  and  nuts.  If  the  laps  are  not  held  tight  together, 
material  gets  between  them,  the  bolts  pull  through  the  belt  and  the  belt 
may  break  across  the  line  of  bolt  holes.  To  prevent  this,  the  bolts  must 
be  kept  tight,  especially  those  at  the  ends  of  the  laps. 


264  FASTENING  BUCKETS  TO  BELT 

In  stone  elevators,  sand  and  grit,  getting  between  the  laps,  has  been 
known  to  grind  the  belt  partly  through  until  it  broke.  The  same  thing  has 
happened  when  an  end  of  belt  at  the  lap  was  not  cut  off  close  to  the  bolts; 
bits  of  stone  wedged  behind  the  projecting  flap  of  belt  and  finally  cut  the 
belt  so  badly  that  it  broke.  In  this  particular  case  the  belt  was  12-ply 
and  was  lapped  the  wrong  way  for  the  travel  of  the  belt.  The  right  way  is 
shown  in  the  figure ;  the  cut  end  of  belt  on  the  inside  of  the  lap  should  trail 
over  the  pulleys,  not  run  against  them. 

Butt-strap  Joints. — The  ends  of  heavy  belts  are  frequently  butted  and 
the  joint  made  by  a  piece  of  belting  as  wide  as  the  elevator  belt  and  two 
or  three  times  as  long  as  it  is  wide.  In  elevators  with  spaced  buckets  the 
length  of  the  butt-strap  may  be  twice  its  width  and  it  is  riveted  on.  In 

continuous  bucket  elevators  it  usu- 
ally extends  under  two  buckets  on 
each  side  of  the  butt  and  is  secured 
^/  by  the   bucket    bolts    (Fig.    247). 

Fi^T-Butt-strap  Joint.  This  J°int  has  the  same  merits  and 

the    same    defects    as    the  lapped 

joint  mentioned  above;  in  addition,  a  bucket  may  have  to  be  left  off  at 
the  joint  to  make  room  for  the  double  row  of  bolts  where  the  ends  of  the 
belt  come  together.  These  bolts  must  be  close  to  the  cut  ends  of  the  belt 
to  prevent  material  from  working  in  between  the  belt  and  the  butt-strap, 
and  they  must  be  kept  tight. 

The  Jackson  belt  fastener  (Fig.  248)  consists  of  a  series  of  stamped  steel 
plates  each  with  two  countersunk  head  bolts,  two  oval  cup  washers  with 
prongs,  and  two  sleeve  nuts.  The 
ends  of  the  belt  are  cut  square  with  a 
thin  piece  of  canvas  belt  as  a  templet; 
the  bolt  holes  are  punched  in  them. 
The  bolts,  with  the  oval  washers  on 
them,  are  inserted  from  the  pulley 
side  of  the  belt;  then  on  the  bucket 
side,  the  canvas  templet  is  laid  for  a 
cushion  and  the  plates  are  put  on. 
When  the  nuts  are  screwed  tight,  the  Ro-  248--Elevator  Belt  Joined  with 

„  x.      .    .,          .    ,  Jackson  Fasteners. 

cup  washers  pull  the  belt  up  into  the 

concaves  of  the  top  plates,  the  sleeve  part  of  the  nut  wedges  the  warp 
threads  together  and  the  belt  is  held  tight.  The  shape  of  the  top  plates 
is  such  that  the  two  bolts  do  not  stand  parallel  to  each  other,  but  at  an 
angle  to  make  them  approximately  radial  in  passing  around  pulleys  of  a 
size  suited  to  the  fastener.  This  prevents  the  bolts  from  moving  in  the 
belt  or  tearing  it  in  passing  over  pulleys. 

The  Jackson  joint  is  made  for  all  thicknesses  of  belts;  it  is  strong,  and 
when  applied  to  stiff  thick  belts,  it  is  not  apt  to  injure  them  as  sometimes 
happens  with  lap  joints  or  butt-strap  joints.  It  is  one  of  the  best  joints 
for  stitched  canvas  or  balata  elevator  belts. 


BUTT-STRAP  JOINTS 


265 


Fig.  249  shows  a  butt-strap  joint  which  has  been  used  on  belts  handling 
very  gritty  material.  The  ends  are 
joined  by  a  metal  fastener  of  sqine 
kind,  and  a  strip  of  belt,  usually 
lighter  than  the  elevator  belt,  is 
placed  over  the  joint  and  under  the 
buckets  to  act  as  a  cushion  for  the 
latter,  to  protect  the  metal  fastener 
from  the  grit  and  also  to  strengthen  the  joint. 


FIG.  249.— Elevator  Belt  with  Bolted 
Fastener  and  Butt-strap. 


CHAPTER  XX 
DRIVING  BELT  ELEVATORS 

Drive  by  Head  Pulleys. — In  the  design  of  a  belt  and  bucket  elevator 
the  diameter  of  the  head  wheel  must  always  be  considered  in  connection 
with  its  speed;  the  two  are  not  independent,  but  for  a  good  discharge  of 
materials,  they  hold  rather  definite  relations  to  each  other.  These  relations, 
for  the  usual  working  conditions,  are  given  in  Tables  35,  36  and  37,  and 
the  conditions  for  which  it  is  proper  to  use  these  tables  are  described  on 
pages  217,  218  and  219. 

The  theory  of  belt  driving  is  based  on  the  assumption  that  so  long  as  the 
belt  bends  freely  to  the  curvature  of  the  pulley  the  driving  effect  is  inde- 
pendent of  the  diameter  of  the  pulley.  This  is  confirmed  in  practice  and 
by  Haddock's  experiments  referred  to  in  Chapter  V.  If  the  diameter  of 
the  pulley  is  at  least  four  or  five  times  the  number  of  plies  in  the  belt, 
the  tractive  effect  does  not  vary  with  the  size  of  the  pulley;  hence  the 
general  rule  is  that  a  6-ply  belt,  for  example,  should  have  a  head  pulley 
at  least  24  inches  in  diameter,  better  still  30  inches,  and  so  far  as  the  internal 
wear  in  the  belt  is  concerned,  the  larger  the  diameter  the  better.  It  is, 
however,  a  fact  that  most  elevator  belts  fail  for  reasons  other  than  internal 
wear,  and  there  are  disadvantages  in  making  the  head  pulleys  too  large; 
the  head  group  takes  up  too  much  space,  the  head  chute  drops  lower,  the 
casing  is  larger,  supports  become  heavier,  larger  driving  machinery  is 
needed,  and  for  most  of  these  items  the  cost  is  greater. 

The  driving  contact  between  a  head  pulley  and  an  elevator  belt  depends 
upon  the  angle  of  wrap  and  the  coefficient  of  friction  between  the  belt  and 
the  rim  of  the  pulley.  Usually  the  angle  of  wrap  is  180°;  hence  the  general 
expression  for  the  ratio  of  tensions  on  the  up-side  TI  and  the  down-side  T2 

Ti 

(seep.  109)  becomes,  for  a  coefficient  of  friction  of  .25,  — =2.19   and  for 

T-i 

T 

a  coefficient  of  .35,  —  =  3.00  (see  Table  20). 
TI 

That  is,  a  head  pulley  will  drive  an  elevator  belt  when  the  pull  on  the 
down  side  is  from  one-half  to  one-third  the  pull  on  the  up  side,  assuming  that 
pulley  and  belt  are  clean  and  dry.  If  the  pull  on  the  down  side  is  more  than 
one-half  the  pull  on  the  up  side,  the  drive  is  more  certain  to  act  under 
unfavorable  conditions,  such  as  dust,  dirt  on  the  belt,  wet  pulley  face,  pulley 
side  of  belt  rough  and  torn,  etc. 

Coefficients  of  Friction. — The  coefficients  .25  and  .35,  mentioned  above, 
are  satisfactory  in  calculations  for  belt  conveyors  and  generally  give  good 

266 


COEFFICIENTS  OF  BELT  FRICTION 


267 


results  in  calculations  for  belt  elevators  also.     The  general  formula  for  the 

Tl  t 

value  of  —  assumes  that/,   the  coefficient  of  friction,  depends  solely  on 

the  nature  of  the  surfaces  in  contact.  Experiments  by  Wilfred  Lewis 
(Transactions  A.  S.  M.  E.,  Vol.  7)  show  that  as  the  load-  increases  and 
Ti  —  Tz  becomes  greater,  the  coefficient  of  friction  also  increases,  although 
the  belt  creep  and  the  belt  slip  increase  at  the  same  time.  Table  50 
abstracted  from  Carl  Earth's  comment  on  the  Lewis  experiments  (Transac- 
tions A.  S.  M.  E.,  1909)  gives  in  column  7  values  of  /  for  leather  belts  on 
clean  iron  pulleys  at  800  feet  per  minute;  they  vary  from  .25  to  .72. 

These  experiments  were  made  with  clean  leather  belts;  but,  reasoning 
from  the  known  behavior  of  various  kinds  of  belt  in  the  transmission  of 
power,  there  is  no  reason  to  think  that  rubber  or  other  fabric  belts  would 
act  differently,  except  for  possible  differences  in  the  numerical  values  of 
the  coefficient  of  friction.  It  is  probable  that  the  coefficients  for  these 
belts  on  clean  iron  pulleys  or  on  pulleys  covered  or  lagged  with  rubber  are 
larger  than  .25  and  .35,  respectively,  but  when  the  belt  is  wet,  as  in  elevators 
that  handle  wet  ores,  or  when  it  becomes  covered  with  granules  of  dirt,  or 
when  the  interior  of  the  casing  is  thick  with  dust  as  in  grain  elevators,  then 

TABLE    50.— VARIATION   OF    COEFFICIENT    OF    BELT     FRICTION    WITH 
SLIP  AND  CREEP  ON  DRIVING  PULLEY 


1 

2 

3 

4 

5 

6 

7 

Tension  per 

Tension  per 

Tension  per 

Observed 

Calculated 

Coefficient  of 

Experi- 

Square Inch 

Square  Inch, 

Square  Inch, 

Loss  in  Slip 

Loss  Due  to 

Belt  Friction 

ment 

Belt 

on 

on 

and  Creep 

Creep  Alone. 

Corrected  for 

Number 

at  Rest. 

Tight  Side. 

Slack  Side. 

Per  Cent  of 

Per  Cent  of 

Centrifugal 

Pounds 

Ti=  Pounds 

Tz  =  Pounds 

Belt  Travel 

Belt  Travel 

Force 

60 

81.6 

125.33 

58.67 

0.5 

0.41 

0.25 

61 

81.6 

131.42 

46.58 

0.9 

0.53 

0.34 

62 

81.6 

142.00 

42.00 

1.7 

0.62 

0.41 

63 

81.6 

152.41 

35.75 

3.0 

0.73 

0.49 

65 

81.6 

179.92 

29.92 

12.0 

0.91 

0.61 

66 

127.5 

177.42 

77.42 

0.5 

0.52 

0.27 

68 

127.5 

198.25 

64.92 

0.8 

0.69 

0.37 

69 

127.5 

208  .  77 

58.67 

1.0 

0.77 

0.42 

70 

127.5 

219.08 

50.75 

1.7 

0.87 

0.47 

71 

127.5 

229  .  50 

46.17 

2.6 

0.95 

0.54 

72 

127.5 

244.08 

44.08 

3.8 

1.02 

0.57 

73 

127.5 

256  .  58 

39.92 

3.5 

1.10 

0.62 

74 

127.5 

252.42 

35.75 

8.6 

1.13 

0.68 

75 

127.5 

283.66 

33.67 

15.2 

1.25 

0.72 

128 

343.5 

511.3 

227.0 

0.5 

0.85 

0.26 

131 

343.5 

557.0 

187.2 

1.1 

0.99 

0.35 

133 

343.5 

589.5 

162.4 

1.8 

1.30 

0.41 

134 

343.5 

603.0 

148.2 

2.7 

1.39 

0.45 

135 

343  .  5 

618.0 

134.0 

5.1 

1.49 

0.49 

NOTE. — Since  1-ply  thickness  in  a  rubber  or  canvas  belt  is  about  ^  inch,  divide  the 
figures  in  column  2  and  3  by  16,  to  estimate  the  equivalent  tension  per  inch  per  ply  in  the 
belts,  had  they  been  of  fabric  instead  of  leather. 


268 


DRIVING  BELT  ELEVATORS 


the  coefficients  are  less  than  for  clean  pulleys.  How  much  less  we  do  not 
know.  Haddock,  in  1908,  made  experiments  (Transactions  A.  S.  M.  E., 
Vol.  30)  with  a  12-inch  4-ply  belt  wrapped  180°  on  plain  and  rubber-covered 
pulleys  dusted  or  coated  with  various  substances;  but  his  values  (see 
Table  51)  are  quite  erratic  and  can  only  be  taken  to  show  that  the  coefficients 
are  less  when  the  pulley  rim  is  dusty  or  damp  than  when  it  is  clean. 

For  dusty  work  the  coefficients  of  friction  for  rubber  or  fabric  belts  on 
iron  pulleys  may  be  taken  at  .20,  and  for  rubber-covered  pulleys  .27.     For 

T7 
these  values  the  corresponding  ratios  of  —  are  1.87  and  2.33,  respectively. 

For  wet  work,  the  coefficient  may  be  called  .20,  whether  the  pulley  is  bare 
or  lagged. 

TABLE   51.— TRACTIVE   EFFECT   EXPRESSED   AS    PERCENTAGES   BASED 
ON  CLEAN  DRY  SURFACES  OF  RUBBER  BELT  AND  IRON  PULLEYS 

(Haddock's  Experiments,  1908—) 


Condition  of  Contact  Surfaces 

Rubber  Belt 
on  Iron  Pulley. 

Per  Cent 

Rubber  Belt 
on  Rubber 
Lagged  Pulley 
Per  Cent 

Clean,  dry  

100 

108 

Clean,  damp  .  .  . 

92 

101 

Covered  with  dry  coal-dust.  .  .  . 

92 

80 

Covered  with  damp  coal-dust 

76 

52 

Covered  with  dry  clay    . 

63 

55 

Covered  with  damp  clay   .  .  . 

55 

65 

Covered  with  dry  slate-dust 

68 

138 

Covered  with  damp  slate-dust  .... 

85 

147 

Covered  with  dry,  sharp  sand 

42 

80 

Covered  with  damp,  sharp  sand  

62 

80 

It  is  certain  that  a  pulley  covered  with  rubber  belt  will  pull  more  than  a 
plain  iron  pulley  if  the  work  is  dry,  and  although  some  engineers  doubt  the 
value  of  lagging  on  head  pulleys  of  wet  elevators,  there  are  some  practical 
advantages  in  it,  even  though  it  may  not  increase  the  value  of  /,  the  coef- 
ficient of  belt  contact.  When  belts  wear  down  to  the  fabric  on  the  pulley 
side  and  become  rough,  and  when  bolt  heads  project  beyond  the  belt  sur- 
face, then  the  contact  with  an  iron  face  is  not  continuous,  but  interrupted, 
and  the  belt  if  wet  is  more  likely  to  slip;  but  if  the  pulley  is  covered,  the 
rim  accommodates  itself  better  to  these  irregularities  and  the  driving  con- 
tact is  better.  This  is  especially  true  if  the  lagging  is  not  ordinary  friction- 
surface  rubber  belt,  but  standard  belt  lagging  which  is  several  plies  of 
fabric  covered  with  a  layer  of  rubber. 

The  application  of  the  above  to  the  design  of  an  elevator  can  be  discussed 
best  by  reference  to  an  example. 

Pull  at  Head  of  Grain  Elevator. — The  unbalanced  torsional  pull  at  the 
rim  of  the  head  pulley,  which  measures  the  power  required  to  drive  the 
elevator  belt,  is  the  sum  of  several  items: 


CALCULATION  OF  PULL  FROM  POWER  READINGS  269 

1.  Weight  of  grain  in  the  lifting  buckets  =G. 

2.  Drag  of  buckets  through  the  grain  in  the  boot  =  B. 

3.  Friction  of  foot  shaft  and  pulleys  =F. 

The  total  pull  in  the-elevator  T5elt  is  the  torsional  pull  plus  the  weight 
of  belt  and  buckets  on  the  rising  side. 

It  is  easy  to  calculate  item  G  directly,  but  not  B  and  F.  F  is  small  and 
may  be  estimated,  but  B  must  be  derived  indirectly  from  power  tests  of  the 
elevator. 

Calculation  of  Pull  from  Power  Readings. — A  certain  grain  elevator 
had  a  nominal  capacity  of  12,000  bushels  per  hour;  the  calculated  capacity 
based  on  all  buckets  lifting  their  full  load  and  discharging  it  without  spill 
was  14.560  bushels  per  hour.  When  the  following  test  was  made,  the 
elevator  was  lifting  wheat  at  its  regular  rate;  assuming  a  possible  loss  of 
10  per  cent  in  filling  the  buckets  and  in  spill  at  the  head,  the  work  was 
probably  at  the  rate  of  about  13,000  bushels  per  hour.  The  lift  was  216 
feet. 

Power  delivered  to  the  motor  80  kilowatts 

80  kilowatts  =  80*4100°  -  107 . 2  h.p. 

Motor  loss  (efficiency  about  94  per  cent)  =6.4  h.p. 

Estimated  loss  in  silent  chain  drive,  countershaft 

and  rope  drive  =5. 4  h.p. 

Estimated  loss  in  turning  head  shaft  at  700  feet 

per  minute  belt  speed  =2.4  h.p. 


Total  losses  up  to  elevator  belt  14 . 2  h.p. 

Power  delivered  to  elevator  belt  93  h.p. 

Horse-power  to  lift  13,000  bushels  wheat  at  60 

pounds  per  bushel  to  height  of  216  feet 
Estimated  loss  at  foot  shaft. 


Horse-power  due  to  load  and  foot  shaft  86  h.p. 


Horse-power  to  drag  buckets  through  grain  in  boot  =  B  =  7  h.p. 

Torsional  pull  delivered  to  elevator  belt  = '— =4400  Ibs. 

700 

Weight  of  belt  on  each  side  =216x6.07=1310  Ibs.  1      270Q  „ 

Weight  of  empty  buckets  each  side      =345x4       =1380  Ibs.  J 

T1  =  total  tension  in  up  belt  (no  take-up  tension)  =7100  Ibs. 

T2  =  total  tension  in  down  belt  (no  take-up  tension)  =2700  Ibs. 

Tl 
In  the  example  above,  if  we  assume/ =  .25  and  —  =2.19,  then  for  a  ten- 

TZ 

in  the  down  belt  of  2700  pounds,  the  head  pulley  would  exert  a  pull 


270  DRIVING  BELT  ELEVATORS 

Ti  of  2700x2.19=5900  pounds  in  the  up  belt.  This  is  far  short  of  the 
actual  pull  of  7100  pounds  and  it  is,  therefore,  probable  that  the  elevator 
could  not  have  been  driven  with  a  bare  iron  head  pulley  unless  the  boot 
shaft  were  loaded  or  screwed  down  to  put  an  extra  tension  in  the  belt. 
If  the  boot  shaft  were  loaded  with  2500  pounds,  1250  pounds  added  to 
Ti  and  T2  would  make  them,  respectively,  8350  and  3950  pounds;  then, 

T 

—  =2.12  and  the  plain  iron  pulley  might  have  driven  the  belt. 

1  2 

The  head  pulley  of  this  elevator  was  actually  covered  with  rubber 
lagging;  assuming /  =  .35,  then  if  T  =2700  pounds,  T{  =2700  X3.00  =8100 
pounds.  This  is  an  excess  of  1000  pounds  over  the  actual  pull  in  the  belt 

or  a  margin  of =22  per  cent  above  the  work  of  digging  and  elevating 

44UU 

the  grain. 

Since  the  foot  of  this  elevator  was  loaded  with  about  1000  pounds  by 
a  weighted  take-up  the  normal  values  of  Ti  and  T2  in  operation  were  prob- 
ably about  7600  pounds  and  3200  pounds,  respectively.  If  we  say  that 
/  =  .35,  and  the  ratio  of  tensions  corresponding  to  that  value  is  3.00,  then 
the  pulley  would  exert  a  belt  pull  of  3200x3.00=9600  pounds,  or  an 
excess  of  2000  pounds  oyer  the  normal  value  of  T\  for  such  contingencies 
as  overload  in  the  boot,  loss  of  driving  contact  due  to  dust  in  the  casing,  etc. 
If  /  should  fall  to  .30,  with  3200  pounds  on  the  down  side,  the  pulley  would 
drive  the  belt  with  a  force  of  8200  pounds,  and  there  would  be  a  margin  of 
600  pounds  above  the  normal  value  of  Ti;  if  /  fell  to  .27,  the  pulley  would 
exert  a  pull  of  7600  pounds  in  the  up  belt,  just  enough  to  drive  it. 

Value  of  Take-up  Tension. — When  a  grain  elevator  200  feet  high, 
capacity  12,000  bushels  per  hour,  is  fitted  with  an  automatic  weighted  take- 
up  boot,  the  boot  shaft  may  move  vertically  2  or  3  inches  during  operation 
between  no  load  and  full  load  with  a  good  new  belt.  This  shows  that  the 
elastic  stretch  may  be  1  or  2  inches  per  hundred  feet  in  such  service,  and  it 
also  indicates  that  in  an  elevator  equipped  with  take-up  screws,  it  is  not 
possible  to  maintain  a  fixed  minimum  tension  T2  in  the  down  belt,  when 
part  of  that  load  is  added,  as  is  usual,  at  the  foot.  But  when  T2  is  kept 
constant  by  a  weighted  or  loaded  take-up,  dust  in  the  casing,  or  the  condi- 
tion of  the  belt,  or  of  the  lagging  on  the  pulley  rim  may  cause  /  to  vary 
within  rather  wide  limits  without  affecting  the  certainty  of  the  drive.  If 
Ti  decreases,  Ti  diminishes  also,  but  in  greater  amount,  because  the  working 

T 

ratio  —  is  between  2  and  3.     When  Ti  diminishes,  the  digging  power  of  the 
Tz 

elevator  or  its  lifting  capacity  falls  off,  and  it  may  choke.  Hence,  in  hard- 
worked  elevators,  and  especially  in  those  which  are  wet  or  dusty,  it  is 
important  to  maintain  the  take-up  tension,  preferably  by  weighting  the 
boot  shaft. 

Calculations  of  Belt  Tensions  and  Horse-power. — The  various  items 
which  enter  into  these  calculations  have  been  set  down  in  Table  52;  the 
following  comment  will  explain  what  they  are  and  how  they  should  be  used. 


CALCULATIONS  OF  BELT  TENSIONS 


271 


1 

4) 

. 

o  —  ' 
«•"  0 

1* 

03 

^.g 

J3  ^5 

<D    0 

Is 

& 

• 

I 

-1» 

f  1 

0 

ll 

Horse-power  Requ: 

Item  IX  belt  speed, 
33,000 

Ibs.  per  minuteX  hei 
33,000 

3" 

rH 
hH 

1 

& 

II 

c3  ^J 

Add  a  small  percen 

Estimate  and  add 

S    £ 

fc.2 
a  « 

11 

OJ     02 

-Si 

Total  h.p.  =  sum  c 
3+9  +  12 

If 
|1 

Same  as  Item  21  ph 
per  cent  for  gre 
tion  losses 

.. 

^^ 

^^ 

55 

10 

0? 

J5 

J21 

(V 

^       o 

co 

^-* 

s-^ 

—  ' 

V 

' 

"  — 

^ 

—  ' 

i>, 

§ 

1 

o 

(H 

1 

g 

B 

2 

§ 

a 

Jj 

•fg 

tS 

£H 

S 

S3 

S3 

0 

S3 

1 

§ 

g« 

1"S 

5 

M 

1 

^ 

00 

s 

s 

00* 

§ 

§ 

§ 

I 

g 

I 

tresses  in  Up  Belt 
at  Head  Pulley 

Weight  of  material 
in  buckets 

.2 

Add  as  a  percentage 
of  height  of  lift. 
(See  page  273) 

i 

a    • 

g 

1 

)  Generally  very 
small 

)  Sum  of  Items 
L  +4+7  +  10  +  16 

3-2 

!|  * 

o>  a 

®  ^    « 

5  S 

)  Sum  of  Items 

-4+7  +  10  +  16+22 

m 

o> 

X-V 

£• 

o 

CO 

CO 

o 

<N 

10  T 

•**• 

^ 

J^' 

3 

*-* 

--' 

^ 

w 

£i^ 

o 
'I 

02 

2 

1 

0) 

1 

I 

d 

O2 

o 

^ 

t 

3 

'1 

>J 

3 

& 

a 

O 

a 

& 

$ 

=3 

cB 

a 

a 

2 

ft 

T3 

3 

o 

0 

e3 

a 

a 

| 

a 

o 

-2 

02 

, 

o 

fi 

•33 

c 

1 

1 

1 

d 

c3 

1 

4) 

3 

s 

c 

Q 

*"O 

*j 

xi 

^3 

«j 

<*H 

jl 

"§ 

1 

bC 
_C 

2 

02 

1 

1 

1 

03 

!—  t 

I 

-o 

*"""     02 

O 

t_l 

1 

0 

O 

5 

1 

.2 

1 

_^ 

T3 

c3 

c3 

(T 

c 

a 

O   ^ 

1 

5P 

o 

0 

be 

a 

1 

J 

a 

o 

Distance 

g^ 

M 

1 
1 

h 

i      i 

bO 

1 

3 

5 

O 

£ 

•3 

o 

•c 

£ 

e 

^ 

= 

1 

a  ' 

272  DRIVING  BELT  ELEVATORS 

Item  1.    Pull  due  to  Weight  of  Material. — This  equals 

pounds  of  material  in  1  bucket  X  height  of  elevator  (feet) 
spacing  of  buckets  (feet) 

or,  what  comes  to  the  same  thing,  it  equals 

capacity  of  elevator  (pounds  per  minute)  X  height  of  elevator  (feet) 
belt  speed  (feet  per  minute) 

Item  3.  Horse-power  to  Lift  the  Load. — These  two  expressions  come 
from  multiplying  Item  1  by 

belt  speed  (feet  per  minute) 
33,000 

to  convert  pounds  of  pull  to  horse-power. 

Item  4.  Pull  due  to  Weight  of  Belt  and  Buckets. — The  weight  of 
ordinary  elevator  belt  in  pounds  per  linear  foot  is  approximately  width 
(inches)  X  number  of  plies  X.03.  For  accurate  weights,  see  Tables  4, 
5,  6,  7,  8.  Weights  of  malleable-iron  buckets  are  given  in  Tables  39,  40, 
41,  42.  Weights  of  other  buckets  can  be  taken  from  manufacturers' 
catalogues. 

Item  7.  Pull  due  to  Pick-up. — This  can  be  determined  only  by  experi- 
ence or  experiment.  An  empirical  rule  based  on  long  practice  is  that  the 
pull  required  to  pick  up  coal,  ashes,  ores,  stone  and  similar  coarse  materials 
from  a  take-up  boot  at  the  speeds  of  Table  36  is  about  equal  to  the  weight 
of  the  material  carried  on  12 D  feet  of  belt,  where  D  is  the  diameter  of  the 
foot  wheel  in  feet.  For  example,  if  an  ore  elevator  has  a  2-foot  diameter 
foot  wheel,  the  work  of  pick-up  is  equivalent  to  adding  24  feet  to  the  height 
of  the  elevator. 

Experiments  by  Hanffstengel  (Forderung  von  Massengiitern.  Vol.  1, 
1915)  with  a  short  elevator  inclined  at  30°  from  the  vertical,  having  a 
fixed  bearing  foot  with  a  semi-circular  bottom  and  a  chute  entering  at  the 
level  of  the  foot  shaft,  gave  the  results  shown  in  Table  53.  The  work 
of  pick-up,  stated  as  foot-pounds  per  pound  of  material  elevated,  is  equiva- 
lent to,  and  may  be  expressed  as,  feet  added  to  the  height  of  the  elevator, 
because  the  work  (foot-pounds)  of  elevating  the  material  is  the  work  of 
lifting  the  same  weight  of  material  through  the  height  of  the  elevator. 
The  figures  of  the  table  are  lower  than  those  given  by  the  empirical  rule 
stated  above,  but  it  is  probable  that  the  rule  is  better  suited  to  ordinary 
practice  than  the  results  derived  from  the  laboratory  test. 

Table  53  shows  that  with  lumpy  material  the  power  required  for  the 
pick-up  was  less  when  the  clearance  between  the  bucket  and  the  boot  bottom 
was  small,  but  where  the  material  was  fine,  like  soft  coal  slack,  the  small 
clearance  was  of  no  advantage.  This  points  to  what  is  already  known  from 
practical  experience,  that  is,  that  power  is  saved  in  elevators  for  lumpy 
material  if  the  bottom  clearance  is  less  than  the  least  dimension  of  the 


PULL  DUE  TO  PICK-UP 


273 


TABLE  53.— WORK  OF  PICK-UP  IN  ELEVATOR  BOOT 
(Adapted  from  Hanffstengel) 


I 

Material  Elevated 

Bottom 
Clearance 
in  Boot, 
Inches 

Work  of  Pick-up 
in  Foot-Pounds  per 
Pound   of  Material 

120  Buckets 
per  Minute 

60  Buckets 
per  Minute 

Soft  coal  slack 

2 
2 
2 

4 
more  than  4 
4.2 
3.3 
5.0 
3.0 

4.6 
more  than  4.6 
8.2 
5.0 
10.0 
5.0 

Soft  coal  slack                                                 .  . 

Boiler  house  coal  (crushed)                   

Boiler  house  coal.                             

Coke  (size  not  stated)  

Coke  (size  not  stated)  

pieces  handled,  so  that  they  cannot  wedge  under  the  bucket.  On  the  other 
hand,  however,  small  clearance  cannot  be  maintained  in  a  take-up  boot, 
and  it  is  often  inconvenient  to  use  a  fixed  bearing  boot  or  a  special  boot 
(see  p.  286).  Small  clearance  leads  to  greater  wear  on  the  bottom  sheet 
of  the  boot  and  the  risk  that  the  sheet  may  be  cut  if  the  buckets  are  knocked 
out  of  shape  or  if  the  foot  shaft  settles  from  wear  in  the  bearings.  For  these 
reasons,  it  is  better  to  use  the  empirical  rule  in  estimating  the  work  of 
pick-up. 

In  high-speed  grain  elevators  with  foot  pulleys  one-third  or  one-fourth 
the  size  of  the  head  wheel  the  grain  piles  up  on  the  lifting  side  and  the  pull 
on  the  belt  due  to  pick-up  may  be  equivalent  to  10D  expressed  in  feet  of 
height,  where  D  is  the  diameter  of  the  foot  pulley  in  feet.  That  is,  if  such 
an  elevator,  has  a  72-inch  head  pulley  and  a  24-inch  foot  pulley,  the  pick-up 
is  equivalent  to  adding  20  feet  to  the  elevator, 

With  relatively  larger  foot  pulleys  and  speeds  according  to  Table  36 
the  work  of  pick-up  for  fine  dry  free-flowing  material  may  be  taken  as  6Z). 

In  inclined  elevators  with  spaced  buckets  run  at  the  speeds  of  Table  37 
the  pick-up  is  easier  and  the  pull  may  be  taken  at  4D  instead  of  6D. 

In  continuous  bucket  elevators  run  at  speeds  not  over  150  feet  per 
minute  and  properly  loaded  from  a  chute  the  shock  or  impact  from  loading 
is  not  great  and  the  added  pull  in  the  belt  due  to  it  may  be  taken  at  2D  or 
3D.  But  if  the  feed  is  poor  and  if  the  spilled  material  is  allowed  to  accu- 
mulate under  the  foot  wheel  the  pull  may  be  6D  or  even  more.  The  same 
is  true  if  the  buckets  at  the  loading  point  are  confined  within  steel  plates 
forming  a  stationary  "  loading  leg,"  in  which  case  material  catching  between 
the  buckets  and  the  plates  adds  to  the  pull  on  the  belt. 

Item  10.  Pull  due  to  Friction  Loss  at  Foot. — One  or  2  per  cent  of  the 
total  calculated  pull  in  the  elevator  belt  should  be  enough  to  cover  this. 

Item  15.  Pull  due  to  Power  Transmission  Loss. — Allow  5  per  cent 
for  each  speed  reduction  from  the  source  of  power  through  belts,  chains 
or  cut  gears,  and  10  per  cent  for  each  reduction  through  cast  gearing. 


274  DRIVING  BELT  ELEVATORS 

Item  18.  Allowance  for  Air  Resistance. — Five  per  cent  should  cover 
this  in  high-speed  grain  elevators. 

Item  19.  Proper  Ratios  of  Belt  Tensions. — If  the  elevator  has  a  belt 
wrap  of  180°  on  a  plain  iron  pulley  the  head  pulley  will  drive,  without 
tightening  the  belt,  if  Ti,  which  is  Item  19,  is  not  more  than  2.19  times 
TI,  which  is  Item  20.  If  the  pulley  is  rubber-covered,  then  Item  19  can 
be  3.00  times  Item  20  without  excessive  slip  (see  Table  20,  page  109). 

Item  21.     Total  Horse-power. — This  is  also  equal  to 

(Item  19 -Item  20)  ^ 

—  Xbelt  speed  (feet  per  minute) 
33,000 

plus  the  allowances  added  in  Item  15. 

Item  22.  Calculation  of  Added  Take-up  Tension. — Suppose  Ti  = 
Item  19=2000  pounds  and  Tf2=Item  20=800  pounds,  then  the  ratio  is 

2000 

—  =2.5;  it  is  greater  than  2.19  and  a  plain  iron  pulley  will  not  drive  the 
800 

belt  unless  extra  tension  is  added.  To  find  what  tension  x  must  be  added 
to  each  side  of  the  belt  to  make  77i=2.19772,  we  say  2000+^  =  2.19  (800  +x), 
from  which  £  =210  pounds,  which  is  Item  22. 

Item  23.  Added  Belt  Tension  due  to  Take-up. — The  total  tension 
to  be  added  by  the  take-up  is  420  pounds,  divided  between  the  up  belt 
and  the  down  belt. 

Maximum  Belt  Tension. — The  total  pull  for  which  the  belt  should  be 
selected  is  either  Item  19  or  Item  25. 

If  we  assume  a  unit  tension  p,  then  for  a  belt  of  width  W,  the  number 
maximum  tension  (Item  19  or  25) 

ofphes=  -jiT 

Working  Tensions  for  Belts. — What  is  said  on  page  111  about  unit 
stresses  applies  generally  to  elevator  belts  as  well  as  conveyor  belts.  In 
most  cases  the  stress  can  be  kept  below  25  pounds  per  inch  per  ply  for  32- 
ounce  duck;  but  there  are  many  successful  elevators  in  which  the  unit  stress 
is  30  pounds.  It  should  not  exceed  35  pounds  for  32-ounce  duck,  nor 
40  pounds  for  36-ounce  duck. 

Thickness  of  Belts  as  Determined  by  Wear. — Elevator  belts  for  coarse 
materials  are  usually  made  some  plies  thicker  than  is  necessary  to  transmit 
the  maximum  tension,  because  in  most  cases  the  life  of  the  belt  is  determined 
by  the  external  wear  and  damage  it  receives  (see  p.  249).  An  extra  thickness 
acts  in  such  cases  as  a  protection  against  belt  failure  by  reason  of  loss  of 
tensile  strength;  it  also  gives  the  belt  strength  and  stiffness  to  back  up  the 
bucket  and  prevent  the  bucket  bolts  from  pulling  through  under  severe 
strain.  This  is  shown  by  some  of  the  elevators  listed  on  page  238.  In 
Elevator  1  the  daily  tonnage  would,  if  evenly  spread  over  every  minute 
of  the  twenty-four  hours,  require  each  bucket  to  be  loaded  only  one-fourth 
full.  If  it  is  assumed  that  the  buckets  are  at  times  three-fourths  full,  the 
maximum  tension  corresponding  to  Item  25  is  7500  pounds,  and  if  the  belt 


BELT  SLIP 


275 


is  stressed  to  26  pounds  per  inch  per  ply,  8  plies  are  required.  Actually 
11  are  used.  In  Elevator  2  the  maximum  tension  is  8100  pounds,  requiring 
less  than  9  plies,  but  the  belt  has  12.  ^Similarly  in  Elevator  4,  the  maximum 
tension  corresponding  to  a  toad  three  times  the  average,  based  on  tonnage, 
plus  the  water  carried,  is  6800  pounds;  this  requires  less  than  9  plies,  but  the 
belt  has  12  plies. 

Minimum  Number  of  Plies  in  Belt. — Practical  experience  has  shown 
that  to  give  good  service  belts  should  have  a  certain  minimum  number  of 
plies,  based  on  the  considerations  stated  above,  regardless  of  the  tensile 
strength  required.  Table  54  is  a  fair  statement  of  modern  practice. 

TABLE  54.— MINIMUM  NUMBER  OF  PLIES  IN  ELEVATOR  BELTS 


Material  Elevated 

Width  of  Belt,  Inches 

10  to  18 

20  to  28 

30  and  over 

Grain,    flour-mill    products,    chips,    bark,    materials 
not  abrasive  
Fine  material,  50-75  Ibs.  per  cu.  ft.,  materials  not  too 
coarse 

4 

5 
6 

5 

6 

7 

6 

7 
8 

Heavy,  coarse  materials,  ore,  crushed  stone,  lump  coal. 

Belt  Slip. — When  a  belt  slips  on  the  head  pulley  there  is  a  reduction  of 
elevating  capacity  and  the  danger  of  a  choked  boot  if  the  feed  continues 
at  the  normal  rate.  In  this  case  the  belt  may  slow  down,  pull  some  buckets 
off  and  eventually  stop.  Even  though  slip  may  not  come  to  the  point  at 
which  the  belt  stops,  wear  on  the  pulley  side  of  the  belt  is  sure  to  follow. 
In  a  rubber  belt  the  duck  on  one  side  may  be  frayed  or  worn  off.  In  a 
stitched  canvas  belt  the  same  thing  happens  or  the  rubbing  glazes  the  sur- 
face on  the  pulley  side  of  the  belt  if  it  has  been  painted,  and  if  it  has  been 
impregnated  with  a  Class  1  compound  (see  p.  47)  the  heat  generated  by 
the  rubbing  is  apt  to  dry  up  the  compound  and  make  the  belt  brittle.  This 
is  not  true  of  Class  2  compounds,  because  they  resist  the  action  of  heat 
much  better. 

The  rubber  covering  of  head  pulleys  is  subject  to  the  same  wear  as  the 
belt,  but  since  the  lagging  exposes  less  surface  to  it  than  the  belt,  the  damage 
is  apt  to  be  greater.  The  heads  of  the  bucket  bolts  often  tear  the  lagging 
when  slip  occurs,  and  with  that  is  combined  the  wear  due  to  belt  creep 
(seep.  276). 

Fig.  238  shows  bolts  used  to  fasten  rubber  lagging  to  the  rim  of  a  grain- 
elevator  head  pulley.  Some  are  bent  by  the  pull  on  the  lagging,  and  the 
heads  are  worn  off  by  the  slip  and  creep  of  the  elevator  belt.  Wearing 
away  the  metal  causes  damage  to  the  pulley  side  of  the  belt  which  adds 
to  that  caused  by  slip  and  creep. 

If  the  choke  is  so  bad  that  the  belt  stops,  it  is  important  that  the  pulley 
should  stop.  also.  In  modern  elevators  with  separate  electric  motor  drive 


276 


DRIVING  BELT  ELEVATORS 


an  overload  release  device  can  be  used  to  throw  off  current  and  stop  the 
motor  if  the  load  becomes  too  great;  but  in  old-time  elevators,  driven  from 
line  shafts,  it  has  often  happened  that  a  head  pulley  continued  to  turn  when 
the  belt  was  stopped  by  a  choke  and  the  belt  was  worn  in  two  by  the  pulley 
and  fell  down  the  legs.  In  some  cases  the  damage  was  more  serious; 
the  friction  from  the  revolving  pulley  set  fire  to  the  belt,  the  flame  caused 
a  dust  explosion  in  the  elevator  casing  and  from  that  followed  loss  of  life 
and  a  fire  which  caused  the  total  destruction  of  the  building  and  its  con- 
tents (see  p.  302). 

Belt  Creep;  Belt  Slip. — When  an  elevator  belt  is  so  heavily  loaded  that 
the  head  pulley  will  not  drive  it  the  belt  may  stand  still  while  the  pulley 
turns  within  the  loop.  The  slip  in  such  a  case  may  be  called  100  per  cent 
of  belt  travel,  because  the  travel  of  the  belt  has  fallen  to  zero.  If  the 
load  is  less,  the  slip  is  less,  but  it  is  always  there  to  some  degree,  although 
it  may  amount  to  only  a  fraction  of  1  per  cent  of  belt  travel  when  the  load 
is  light  (see  also  Chapter  V). 

Belt  creep  is  different.  In  Fig.  250,  representing  the  head  of  an  elevator, 
the  up  belt  under  tension  T\  assumes  a  certain  stretch,  so  that  a  section  of 
belt  normally  12  inches  long  under  no  load  may  be  pulled  to  12|  inches  long 

just  as  it  reaches  the  pulley.  A  second 
or  two  later  that  section  of  belt  has 
reached  the  other  side  of  the  pulley, 
the  tension  has  fallen  to  T2  and  the 
length  is  only  12^6  inches — that  is, 
in  passing  over  the  pulley,  every  foot 
of  elevator  belt  shortens  y£  inch,  and 
if  the  belt  speed  is  640  feet  per 
minute,  the  creep  or  relative  move- 
ment between  the  belt  and  the  rim  of 
the  pulley  is  40  inches  per  minute  or 
114  miles  per  year  of  average  service. 
An  illustration  of  belt  creep  sug- 

gested  b^  W'  W'  Bird  (Transactions 
A.  S.  M.  E.,  1905)  is  to  stretch  an 
ordinary  elastic  band  as  a  belt  over  two  small  pulleys  of  equal  size.  If 
the  band  has  any  resistance  to  overcome,  the  driven  pulley  may  turn  only 
half  as  fast  as  the  driver.  In  this  case  the  50  per  cent  loss  in  transmission 
is  not  due  to  slip  at  all,  it  is  due  to  the  creep  of  the  highly  elastic  band  on 
the.  pulleys. 

The  relations  between  slip  and  creep  and  load,  as  observed  in  some  of 
Wilfred  Lewis's  experiments,  are  given  in  Table  50  (see  p.  267).  Col- 
umn 5  states  the  combined  slip  and  creep  in  per  cent  of  belt  travel  as  regis- 
tered by  the  apparatus  used  in  the  tests.  In  Column  6  Barth  has  calculated 
the  creep  alone  from  the  observed  stretch  of  leather  belts  under  load.  In 
Lewis's  experiments  no  tests  were  made  of  rubber  or  other  fabric  belts,  but 
so  far  as  creep  and  slip  are  concerned,  it  is  probable  that  the  differences 


Original  Length 
Length  at 

..          „    Tz 
Belt  Creep  per  Ft. 


FIG.  250.— Creep  at  Head  of  Belt  Elevator. 


EFFECT  OF  CREEP  AND  SLIP  277 

between  leather  belts  and  fabric  belts  would  be  in  degree  only,  and  not  in 
manner.  Assuming  that  the  differences  are  not  great,  we  can  take  an 

example  from  Tests  128  -and  ISl^Table  50.      Here  the  ratios  of  —  are 

T2 

between  2  and  3,  as  in  general  elevator  practice,  and  the  tension  in  the  belt, 
511  or  557  pounds  per  square  inch,  corresponds  to  between  30  and  35  pounds 
per  inch  per  ply  of  fabric,  which  is  not  unusual  in  elevator  belts.  Here  the 
combined  slip  and  creep  (see  Column  5)  amounts  to  0.5  to  1.1  per  cent  of 
belt  travel,  and  by  calculation  practically  all  of  it  is  creep.  It  may  be 
said  then  that  in  elevator  practice  a  creep  of  at  least  \  of  1  per  cent  is 
unavoidable. 

If  the  load  on  the  elevator  belt  is  increased,  T\  would  increase  and 
the  belt  might  slip,  unless  T2  were  increased  by  putting  more  tension 
on  the  belt  by  screwing  down  or  loading  the  boot  shaft.  Then  with  a  clean 
belt,  the  coefficient  of  driving  contact  might  rise  slightly  (see  Experiment  133, 
Column  7),  and  the  head  pulley  would  drive  the  belt,  but  with  0.5  per  cent 
slip  plus  1.3  per  cent  creep.  This  sum  represents  a  loss  of  nearly  2  per  cent 
of  belt  travel;  it  shows  what  may  happen  in  an  elevator  severely  overloaded. 

Effect  of  Creep  and  Slip. — It  is  doubtful  whether  the  coefficient  of  belt 
friction  in  the  instance  mentioned  above  would  increase  in  the  same  propor- 
tion in  a  wet  or  dusty  elevator;  but  in  any  case,  the  slip  is  objectionable. 
It  means  not  only  a  loss  of  elevator  capacity,  but,  what  is  more  injurious, 
a  movement  between  the  pulley  rim  and  the  belt,  which,  under  the  pressure 
due  to  the  load  at  the  head  of  the  elevator,  tends  to  wear  away  the 
pulley  side  of  the  belt,  or  the  lagging  of  the  pulley,  if  it  is  rubber- 
covered. 

Lagging  on  head  pulleys  does  not  last  as  long  as  the  elevator  belt; 
the  two  materials  are  usually  of  the  same  class  of  belting,  but  the  wear  on 
the  belt  is  spread  over  perhaps  100  to  400  feet  of  length  while  the  wear  on 
the  pulley  covering  is  confined  to  10  to  25  feet  of  lagging.  Besides,  the 
lagging  is  often  worn  and  torn  by  the  heads  of  the  bucket  bolts  projecting 
beyond  the  pulley  side  of  the  belt,  especially  when  the  bolts  are  loose  or 
the  belt  worn.  The  wear  is  also  greater  when  the  elevator  belt  is  of  poor 
quality  or  too  thin  for  the  work;  a  belt  that  stretches  greatly  under  load 
will  creep  more  on  the  head  pulley  than  a  firm  belt,  not  overloaded,  from 
which  the  excess  elasticity  of  the  fabric  has  been  removed*  during  the 
process  of  making  the  belt. 

Pulleys  with  Rough  Rims,  or  rims  not  turned,  or  rims  cast  with  depres- 
sions or  slots  parallel  to  the  shaft  have  been  used  in  elevators  to  increase  the 
grip  on  the  belt.  It  is  doubtful  whether  the  coefficient  of  belt  contact  on 
such  a  pulley  is  any  greater  than  on  a  smooth  rim,  but  there  is  no  doubt 
that  when  a  belt  creeps,  as  it  must,  or  when  it  slips,  as  it  may,  it  is  sure  to 
be  damaged  by  the  rough  rim.  If  the  elevator  is  overloaded,  so  that  the 
belt  stops  while  the  pulley  continues  to  turn,  a  rough  rim  may  ruin  a  belt 
in  a  few  minutes.  The  same  thing  may  happen  if  the  elevator  is  started 
under  load  and  with  a  choked  boot,  as  a  result  of  an  enforced  shut-down 


278  DRIVING  BELT  ELEVATORS 

caused  by  failure  of  electric  power,  or  by  some  mishap  to  the  elevator  ma- 
chinery or  its  accessories. 

In  the  Western  mining  country,  belt  elevators  are  in  general  use  for 
handling  pulps  and  wet  ores  in  the  process  of  concentrating.  When  the 
mixture  is  largely  water,  the  spill  and  splash  at  the  head  and  the  material 
in  the  boot  keep  the  belt  and  pulleys  wet,  the  belt  slips  on  the  head  pulley 
and  is  worn  on  the  pulley  side.  Experiments  have  been  made  with  devices 
to  prevent  slip,  such  as  slatted-faced  pulleys,  rough-rim  pulleys,  etc.,  but 
they  add  to  the  wear  on  the  belt  for  the  reasons  stated  above.  The  real 
cure  for  slip  is  a  strong  belt,  more  tension  in  the  belt  and,  if  possible,  the 
use  of  an  automatic  foot  take-up  to  maintain  that  tension.  On  this  point, 
see  page  299. 

Patents  have  been  issued  on  pulleys  with  projecting  cleats  or  buttons 
and  on  pulley  lagging  with  a  roughened  face.  None  of  these  devices  would 
work  at  the  head  of  an  elevator.  The  belt  must  creep  and  it  may  slip; 
any  bodily  interference  with  these  natural  movements  will  injure  the  belt. 

Elevator  Head  Pulleys  are  sometimes  made  split,  that  is,  in  halves,  for 
convenience  in  handling  or  getting  on  or  off  the  shaft;  but  when  they  are 
made  in  the  ordinary  way  with  the  heads  and  nuts  of  the  clamping  bolts 
bearing  against  rough  unfinished  surfaces  the  bolts  are  apt  to  work  loose 
under  vibration  and  heavy  loads.  For  important  work,  split  pulleys  should 
have  finished  bearing  pads  around  the  bolt  holes  at  hub  and  rim.  Some 
engineers  will  not  use  split  pulleys  at  all,  but  specify  clamp  hub  pulleys 
fitted  with  not  over  .002-inch  clearance  to  a  shaft  turned  to  accurate  size. 
When  standard  grade  pulleys  are  put  on  cold  rolled  or  turned  shafting  of 
commercial  grade  the  clearance  may  be  .005  inch  or  more,  and  very  often 
the  pulley  works  loose  and  shifts  on  the  shaft  in  spite  of  keys  and  set  screws. 
Some  engineers  have  their  head  pulleys  bored  a  few  thousandths  smaller 
than  the  accurately  turned  shaft  and  then  pressed  or  driven  on;  others  use 
clamp  hub  pulleys,  heat  the  hub  bolts  nearly  to  redness,  put  them  in  place, 
tighten  the  nuts  and  let  the  contraction  of  the  bolts  clamp  the  hub  even 
tighter  and  prevent  the  nuts  from  loosening.  In  some  large  ore  elevators 
(Ohio  Copper  Co.,  Lark,  Utah,  Eng.  and  Min.  Jour.,  Vol.  99)  the  head  pul- 
leys are  60  by  38  inches,  split,  bored  5j^  inches  with  2  keys  at  90°  apart, 
and  the  outside  of  the  hub  at  each  end  is  turned  to  take  a  f  by  5-inch  welded 
steel  band  shrunk  on.  These  pulleys  stay  tight;  to  remove  them,  the  bands 
must  be  cut  apart. 

Lagging  consists  usually  of  3-  or  4-ply  rubber  belt  fastened  on  by  £-inch 
flat-head  bolts.  It  is  important  that  the  bolt  heads  should  be  below  the 
surface  of  the  lagging;  for  this  reason  the  pulley  rim  should  be  countersunk 
around  the  bolt  hole  to  allow'  the  belt  to  be  depressed  (see  Fig.  104,  p.  123). 
Pulley  faces  up  to  18  or  24  inches  can  be  covered  by  a  strip  of  belt  of  that 
width;  for  wider  faces  and  heavy  crowns  it  is  easier  to  use  two  strips  of 
belt  of  half  the  width. 

An  improved  pulley  lagging  consists  of  2-  or  3-ply  rubber  belt  with  a 
cover  YQ  or  I  mcn  thick.  This  does  not  cost  more  than  4-ply  belt,  it  resists 


ELEVATOR  HEAD  PULLEYS 


279 


abrasion  better  and  is  not  so  likely -to  be  injured  by  projecting  heads  of 
bucket  bolts  (Fig.  238).  On  the  wear  of  lagging,  see  page  250. 

Face,  or  Width,  of  Head  Pulleys  ife  usually  1  or  2  inches  more  than  bolt 
width,  up  to  30  or  36  inches  and  3  or  4  inches  more  for  wider  belts.  The 
excess  of  face  permits  the  belt  to  run  out  of  center  for  an  inch  or  two,  in 
case  the  head  shaft  is  not  leveled  properly  or  gets  out  of  level  by  shrinkage 
or  settling  of  supports. 

The  crown  of  standard  transmission  pulleys  is  £  inch  on  the  diameter 
per  foot  of  face — that  is,  the  face  of  a  pulley  for  a  12-inch  belt  is  Y&  inch 
higher  in  the  middle  than  at  the  edges.  In  most  cases,  elevator  head  and 
foot  pulleys  are  made  in  the  same  way,  but  some  engineers  prefer  a  crown  of 
YQ  inch  per  foot  or  even  £  inch  per  foot  for  the  head  pulleys  of  elevators  that 
are  hard  to  keep  in  alignment.  When  the  belts  are  wide  and  the  buckets 
are  in  single  row  the  extra  high  crown  may  be  objectionable  (see  p.  261), 


Oh . 


TABLE  55.— RIM  THICKNESS— INCHES,  OF  STANDARD 
D.  B.  PULLEYS 


Diam- 
eter, 
Inches 


WIDTH  OF  BELT  —  INCHES 


12 


14 


16 


18 


20 


22 


24          28 


32 


36 


40 


30 


36 


42 


48 


D  _ 


54 


60 


66 


5  = 


5  =  f 


5  =  1 


5  = 


72 


5 


5  = 


84 


A.  ==- 
D  _ 


r>  _  1 
-O  —  1 


96 


T>  _    1 


A-l 

5  = 


5  = 


TJ   _ 


5=1 


5=1 


280  DRIVING  BELT  ELEVATORS 

but  this  is  not  so  when  the  buckets  are  bolted  to  the  belt  in  two  rows 
(Fig.  244). 

Flanged  pulleys  should  never  be  used  on  elevators,  either  at  head  or 
foot.  Contact  between  the  flanges  and  the  edges  of  the  belt  will  cut  or 
wear  off  the  edges. 

Rims  of  Head  Pulleys  are  not  turned  to  exact  widths  or  thicknesses, 
and  the  dimensions  vary  with  different  makers.  Table  55  gives  approx- 
imate thicknesses  of  double-belt  pulleys  at  the  edge  and  center  of  rim  for 
the  sizes  generally  used  at  the  head  of  centrifugal  discharge  elevators. 
For  high  elevators  handling  grain  and  for  large  elevators  for  minerals  and 
ores  it  is  advisable  to  use  pulleys  with  thicker  rims  and  heavier  arms.  A 
thicker  rim  is  also  recommended  for  cases  where  the  pulley  is  not  lagged 
and  the  belt  handles  wet,  gritty  material.  The  slip  and  creep  of  the  belt 
combined  with  the  grit  which  sticks  to  the  belt  often  wears  out  the  rim 
of  a  standard  pulley.  For  creep  and  slip,  see  page  276. 


CHAPTER  XXI 
ELEVATOR  BOOTS 

Purposes  of  Elevator  Boots. — An  elevator  boot  serves  several  purposes : 

1.  To  confine  the  material  to  the  path  of  the  buckets; 

2.  To  support  the  foot  shaft; 

3.  Generally,  but  not  always,  to  support  the  elevator  casing. 

There  are  two  general  types  of  elevator  boots — boots  with  fixed  shaft 
bearings  and  boots  with  take-up  bearings. 

Fixed  Bearing  Boots. — Where  elevator  pits  are  small,  or  hard  to  get  at, 
or  blocked  at  times  by  spill  from  feeding  conveyors,  or  by  chokes  in  the 
elevator  itself,  it  may  be  an  advantage  to  use  boots  with  fixed  bearings 
and  put  the  take-up  bearings  at  the  head  of  the  elevator.  This  is  standard 
practice  in  some  cement  mills;  the  elevators  are  provided  with  stairs  and 
platforms  which  make  it  convenient  to  reach  the  head  to  adjust  the  take- 
ups.  The  take-up  screws  in  this  position  are  comparatively  clean,  but  in  a 
deep  pit  they  become  dirty  and  hard  to  turn  in  spite  of  dust  guards  and 
ordinary  efforts  to  keep  the  pit  clean.  In  some  mills,  pits  are  never  per- 
mitted to  get  dirty  with  spilled  material;  but  in  others,  with  the  class  of 
labor  employed,  the  great  volume  of  material  handled,  and  the  twenty-four- 
hour  continuous  operation,  it  is  practically  impossible  to  keep  them  clean 
at  all  times. 

Fig.  251  shows  a  pit  for  the  foot  of  an  elevator  for  crushed  cement  rock 
\  inch  and  under.  The  entire  structure  below  the  floor  line  is  concrete, 
the  foot  bearings  rest  in  openings  in  the  8-inch  walls  forming  the  sides  of  the 
boot.  Sheet-steel  doors  on  each  side  give  access  to  the  interior  of  the  boot 
and  a  chute  with  a  slide  door  permits  spilled  material  or  material  which  has 
been  cleaned  out  of  the  boot  to  be  shoveled  from  the  pit  into  the  path  of  the 
buckets. 

There  are  other  reasons  for  using  boots  with  fixed  bearings.  In  a  take- 
up  boot,  with  the  wheel  in  its  upper  position,  there  is  a  mass  of  material 
lying  beyond  the  sweep  of  the  buckets  which  may  pack  so  hard  that  unless 
it  is  dug  loose  by  hand  before  the  wheel  is  set  down  to  a  new  position  the 
buckets  will  not  pick  it  up,  but  will  be  torn  loose  or  pulled  out  of  shape. 
This  is  true  of  some  chemicals  and  fertilizers,  and  of  cement;  for  these,  a 
boot  with  a  definite  sweep  of  the  buckets  is  best.  Fixed  bearing  boots 
are  also  used  for  food  products  which  spoil  if  allowed  to  accumulate  beyond 
the  sweep  of  the  buckets,  also  in  elevators  which  at  different  times  handle 
different  materials  which  should  not  be  mixed. 

281 


282 


ELEVATOR  BOOTS 


If  the  material  handled  is  coarse,  hard  and  lumpy  there  is  some  advantage 
in  using  a  fixed-bearing  boot,  so  that  the  pieces  pushed  by  the  buckets 
slide  over  a  curved  steel  bottom  plate  at  a  fixed  distance  from  the  foot  shaft 
and  do  not  drag  over  a  bed  of  lumps  lying  beyond  the  sweep  of  the  buckets 
(see  p.  273  and  Table  53).  There  is,  however,  a  limitation  to  this;  if 
the  material  is  approximately  round  or  cubical  in  shape,  buckets  can  be 
run  close  to  a  bottom  sheet,  but  if  the  pieces  are  sharp-cornered,  or  angular 
or  long,  like  slivers,  there  is  danger  that  they  may  wedge  between  the  buck- 
ets and  the  bottom  sheet  and  either  damage  the  belt  or  chain  or  tear  the 
bucket  loose  or  punch  a  hole  in  the  sheet.  If  these  materials  are  handled  in 
a  centrifugal  discharge  elevator,  which  is  not  always  the  best  way,  then  the 
clearance  should  be  larger  than  the  dimension  of  the  lump  and  the  bucket 
should  be  large  enough  and  strong  enough  and  the  belt  or  chain  that  carries 
it  sufficiently  powerful  to  dig  the  material  as  if  from  its  own  bed. 


Elevator 
Casing 


-CJ 


Section  CO 


FIG.  251.— Concrete  Pit  and  Boot  for  Pulverized  Stone  Elevator. 

In  many  elevators  for  sand,  ashes,  coke  and  similar  abrasive  substances 
the  boot  is  made  as  the  lower  part  of  the  elevator  casing  and  not  as  a  separate 
piece;  in  these  elevators  it  is  not  customary  to  use  a  curved -bottom  sheet, 
nor  even  a  flat-bottom  sheet;  the  floor  on  which  the  casing  rests  forms  the 
bottom.  This  construction  saves  something  in  first  cost  and  also  in  renew- 
als, for  a  curved  boot  bottom  does  not  last  long  when  the  elevator  handles 
lumpy  and  abrasive  materials. 

In  some  elevators  even  less  attempt  is  made  to  confine  the  material  to 
the  path  of  the  buckets;  in  hot-clinker  elevators,  for  instance,  as  used  in 
cement  mills,  the  boot  consists  of  a  trench  or  pit  with  the  shaft  bearings 
mounted  on  the  side  walls  or  on  cast-iron  pedestals  between  the  walls. 
The  clinker  then  forms  its  own  boot  under  and  alongside  the  foot  wheel. 
Most  of  it  is  like  sand  or  gravel  in  size,  and  even  if  a  large  fused  mass  of 
clinker  or  a  portion  of  dislodged  kiln-lining  too  large  for  the  buckets  should 
slide  down  into  the  pit,  it  will  not  jam  there,  as  the  buckets  can  tumble  it 


VARIOUS  ELEVATOR  BOOTS 


283 


FIG.  252. — Cast-iron  Fixed-bearing  Boot. 
(Jeffrey  Mfg.  Co.) 


out  of  the  way.  These  clinker  elevators  are  chain  machines,  but  the 
arrangement  described  is  applicable  to  some  belt  elevators  as  well. 

Manufacturers'  designs  of  ^fixed 
bearing  boots  are  of  steel  plate 
throughout  or  with  cast-iron  sides  and 
a  steel-plate  bottom.  Fig.  252  shows 
one  which  can  also  be  furnished  with 
a  sectional  cast-iron  bottom  to  take 
the  wear  from  abrasive  materials. 
Fig.  253  shows  a  boot  for  fine  crushed 
rock,  designed  by  a  cement  company 
for  its  own  use;  it  is  fed  at  front  and 
back.  The  j-inch  bottom  sheet  is 
not  fastened  in  place,  but  is  held  in  a 
3^5-inch  slot  between  a  bent  angle  and 

a  bent  flat  fastened  to  each  side  of  the  boot.  The  shaft  bearings  can  be 
easily  removed,  a  retainer  ring  on  the  inside  of  the  boot  holds  the  heads 
of  the  bolts  from  turning  and  keeps  them  from  falling  out  of  place. 

Designers  of  elevators  sometimes 
choose  fixed  bearing  boots  so  that  the 
elevators  can  be  driven  at  the  foot 
without  interfering  with  the  take-up. 
This  is  perhaps  the  poorest  reason 
for  using  such  boots.  Belt  elevators 
carrying  light  stuff,  like  wood  chips, 
have  been  driven  at  the  foot,  but  the 
head  take-ups  need  constant  attention 
to  keep  the  belt  in  driving  contact 
with  the  foot  pulley.  In  chain  ele- 
vators driven  at  the  foot  the  chains 
slip  and  break  unless  they  are  kept 

at  a  steady  tension  and  free  from  slack.  Experienced  engineers  do  not 
drive  elevators  at  the  foot. 

Take-up  Boots. — Over  thirty  styles  of  take-up  boots  are  sold  by  American 
manufacturers,  and  most  of  them  are  made  in  a  number  of  sizes.  There  are 
two  principal  kinds — boots  for  coal  and  similar  coarse,  heavy  substances 
and  boots  for  grain.  The  distinguishing  features  of  these  boots  are 
determined  by  the  pick-up  of  material;  for  a  discussion  of  this,  see 
pages  217,  219. 

Boots  for  Coal  and  similar  coarse,  heavy  materials  consist  of  a  pair  of 
sides,  usually  cast  iron,  joined  by  a  curved  bottom  plate,  usually  of  steel 
plate.  The  front  is  sloped  to  direct  material  into  the  path  of  the  buckets 
and  at  the  same  time  to  form  a  clearance  space  into  which  the  pieces  may 
be  pushed  instead  of  jamming  against  the  bottom  sheet,  as  might  happen 
if  the  bottom  were  fully  rounded  with  the  lower  position  of  the  shaft  as  a 
center. 


FIG.  253. — Double-sided  Boot  for  Pulverized 
Cement  Rock. 


284 


ELEVATOR  BOOTS 


Bottom  Sheet 

FIG.  254. — Cross-section 
through  One  Side  of  a 
Boot  for  Coal  and  Min- 
erals. (Link-Belt  Co.) 


Fig.  254  shows  a  section  through  one  side  of  a  standard  boot.     The 

bearings,  closed  at  the  outer  end  to  prevent  loss  of  lubricant,  are  made  with 
a  spherical  center  so  that  the  shaft  will  not  be 
cramped  even  if  the  two  bearings  are  not  adjusted 
alike,  or  if  the  shaft  is  not  square  with  the  sides  of 
the  boot.  A  rectangular  slide  frame  holds  the  bear- 
ing and  moves  up  and  down  in  a  slot  in  the  side  of 
the  boot;  a  cap  for  the  slide  frame  allows  the  bearing 
to  be  removed  easily.  There  is  a  steel  plate  on  the 
inside  of  the  boot  which  travels  with  the  shaft  and 
keeps  the  slot  closed  in  any  position  of  the  shaft. 
Springs  acting  on  clamp  bolts  keep  the  plate  tight 
against  the  boot  side,  prevent  dust  from  coming 
out  and  keep  material  away  from  the  bearings  and 
the  slides.  The  screw  works  in  a  nut  held  in  a 
recess  in  the  boot  side  by  a  separate  yoke  piece,  a 
small  casting  which  will  break  and  save  the  boot  side 
in  case  of  a  choke  or  an  accident  in  the  boot.  An 
opening,  or  clean-out,  in  each  side  of  the  boot,  is 

closed  by  a   cover,  recessed  to  form  a  dust  seal  and   paneled  inwardly  so 

that  it  comes  flush  on  the  inside  of  the  boot  and  does  not  leave  a  cavity 

or   depression    in  which 

pieces  of  material  might 

be  jammed  and  then  tear 

buckets   off   or    damage 

the  belt.     This  feature  is 

not  important  in  a  grain 

boot,  but  it  is  of  value 

in   a   boot   that  handles 

hard,  coarse  material. 
Dust-tight    Boots.  - 

Other    boots,    in    styles 

similar    to    the    above, 

have  removable  cast-iron 

bottom  plates  for  greater 

durability;  others,  made 

to    be    dust-tight,    have 

covers  outside  the  bear- 
ings in  addition  to  the 

inside  slide   plates  (Fig. 

255).       The-   jaw-levers 

pivoted  to  the  top  of  the 

take-up    screws    give    a 

large  leverage  for  adjust- 
ing the  bearings  and  do  not  interfere  with  the  elevator  casing  as  a  hand- 
wheel  would. 


FIG.  255. — Take-up  Boot  with  Outside  Dust-seals. 


BOOT  TAKE-UPS 


285 


Boot  Take-ups. — When  boots  are  made  as  the  base  sections  of  steel  or 
wood  elevator  casings  the  take-ups  are  necessarily  separate  parts  bolted 
on.  Fig.  256  shows  one  style  rnjgide  with  a  slide  plate  to  keep  the  slot  in 
the  side  of  the  boot  closed  at  all  times. 

When  a  boot  works  in  a  damp  or  wet  place  it  is  advisable  to  make  the 
take-up  nuts  of  brass,  so  that  the  take-up  screws  will  not  rust  tight  in  them. 

Boots  in  Missouri  Lead  Mines. — Standard  boots  listed  by  manu- 
facturers are  well  suited  to  handle  coal  and  other  substances  which  are 
not  too  hard  or  too  abrasive.  With  such  materials,  the  wear  on  the  boot 
sides  and  bottoms  is  not  too  rapid,  but  for  elevators  that  carry  ores  and 
minerals  in  ore-reduction  plants,  concentrator  plants  and  cement  mills, 
the  boots  are  often  of  special  design,  with  the  idea  of  resisting  abrasion 
by  making  the  sides  and  bottoms  very  heavy,  or  else  dispensing  with  iron 


FIG.  256. — Take-up  with  Dust-seal 
for  Steel  or  Wood  Boot. 


FIG.  257. — Boot  for  Crushed  Ore, 
Joplin,  Missouri. 


and  steel  construction  entirely.  In  the  lead-mining  district  of  Missouri 
crushed  ore,  in  size  from  sand  up  to  f  or  £  inch,  is  handled  wet  or  dry  in 
belt  elevators  with  boots  that  consist  of  a  rectangular  box  of  planks  or  a 
concrete  pit  which  in  width  has  a  foot  of  clearance  on  each  side  of  the 
pulley,  and  in  length  has  room  enough  for  a  man  to  get  in  and  use  a  shovel 
behind  the  pulley.  These  boots  may  be  6  or  8  feet  below  the  floor  of  the 
mill.  The  tension  is  put  on  the  belt  and  slack  taken  up,  not  by  screws, 
but  by  the  arrangement  shown  in  Fig.  257.  A  4  by  6-inch  vertical  post 
is  notched  at  the  bottom  end  to  take  the  shaft,  and  the  shaft  turns  in  the 
notch.  A  pivoted  lever,  held  in  position  on  each  side  of  the  wooden  casing 
by  wedges  or  clamp  bolts,  acts  down  on  the  4  by  6-inch  post  and  applies 
pressure  to  the  ends  of  the  foot  shaft.  In  some  of  these  elevators  the  shaft 
has  a  flanged  sleeve  set-screwed  on  it  at  each  end  to  take  the  wear  from  the 
pressure-post;  when  the  sleeve  wears  out  it  is  thrown  away  and  a  new 
one  is  slipped  on.  No  attempt  is  made  to  lubricate  it. 


286 


ELEVATOR  BOOTS 


FIG.  258. — Take-up  Adjustment 
by  Moving  the  Whole  Boot. 


Take-up  by  Moving  the  Whole  Boot. — Fig.  258  shows  a  boot  that  has 
a  take-up  arrangement  and  yet  maintains  a  fixed  clearance  between  the 
sweep  of  the  buckets  and  the  bottom  plate.  The  elevator  handled  crushed 

dolomite;  it  had  to  be  inclined  on  account 
of  the  position  of  the  bin  which  it  fed;  and 
because  of  the  small  space  available,  the 
casing  had  to  be  very  narrow  with  the 
buckets  running  on  guide  angles.  It  was 
necessary  to  prevent  an  accumulation  of 
material  in  the  boot,  and  since  take-ups 
could  not  be  placed  at  the  head,  the  boot 
was  therefore  mounted  on  a  frame  pivoted 
at  one  end  and  adjusted  by  two  bolts  to  give 
the  necessary  take-up  travel. 

Position  of  Feed. — From  what  has  been 
said  in  Chapter  XV  it  is  clear  that  in  a 
centrifugal  discharge  elevator  the  buckets 

take  their  load  on  the  rising  side  of  the  foot  wheel,  and  at  the  ordinary 
speeds  of  Tables  35  and  36,  the  buckets  cannot  take  a  full  load  unless 
they  receive  some  material  at  or  above  the  level  of  the  foot  shaft.  This 
is  especially  true  if  the  foot  wheel  is  smaller  than  the  head  wheel.  How 
this  affects  the  delivery  of  grain  to  buckets  in  a  high-speed  grain  elevator 
has  been  shown  in  Figs.  207  and  208. 

When  a  centrifugal  discharge  elevator  takes  coal  or  some  similar  material 
from  a  sloped-front  boot  the  action  is  very  much  the  same.  Fig.  259 
shows  a  standard  form  of  boot  with  a  front  sloped  at  45°  and  with  the 
lower  edge  of  the  feed  chute  about  level  with  the  center  of  the  foot  wheel 
in  its  upper  position  of  take-up  travel.  When  the  elevator  starts,  and 
material  is  fed  into  the  boot,  little  or  none  of  it  is  caught  by  the  buckets 
until  a  bed  of  dead  material  forms  beyond  the  sweep  of  the  buckets  and 
piles  up  in  the  front  of  the  boot.  If  the  material  is  fine  and  dry  and  stands 
at  a  low  angle  of  repose,  the  bed  of  dead  material  will  not  reach  up  into 
the  chute;  if  it  stands  at  45°,  as  shown  in  the  figure,  it  will  partly  block  the 
chute;  if  it  is  damp  and  sluggish  like  foundry  sand  or  boiler-house  ashes, 
or  bituminous  coal  or  other  material  received  in  open  cars  and  exposed  to 
rain  or  snow,  then  the  angle  of  repose  may  be  so  steep  that  the  chute  will 
be  choked  and  the  flow  of  material  stopped. 

When  the  wheel  is  in  the  lowest  position  of  take-up  travel  (Fig.  260) 
the  boot  is  kept  clear  of  accumulated  material,  and  the  disturbance  of  the 
material  beyond  the  reach  of  the  buckets  on  the  rising  side  of  the  wheel 
prevents  it  from  blocking  the  chute. 

There  are  standard  forms  of  take-up  boot  with  steep  fronts,  the  angle 
being  more  than  45°.  Fig.  261  shows  one  with  a  55°  front  and  with  the 
lower  edge  of  the  feed  chute  above  the  center  of  the  foot  wheel  in  its  upper 
position  of  take-up  travel.  When  the  wheel  in  such  a  boot  is  all  the  way 
up,  the  bed  of  dead  material  beyond  the  sweep  of  the  buckets  will  not 


FEED  INTO  TAKE-UP  BOOTS 


287 


back  up  in  the  chute  unless  it  stands  at  a  steep  angle,  and  hence  this  boot 
is  likely  to  work  better  than  a  Ibw-front  boot  if  the  material  is  damp,  slug- 
gish or  apt  to  pack  hard  and  staad  on  a  steep  angle  of  repose.  When  the 
wheel  is  in  its  lowest  position  (Fig.  262)  there  is  even  less  chance  of  a  choked 
chute,  and  the  buckets  fill  well. 

One  drawback  of  a  steep-front  boot  is  that  when  the  take-up  is  all 
the  way  down,  an  excess  of  feed  over  elevator  capacity  may  cause  the  foot 
wheel  to  be  buried  so  deep  that  the  buckets  cannot  dig  themselves  free. 
This  may  happen  if  a  heavy  load  is  dumped  into  the  boot  or  if  the  elevator 
should  slow  down  or  stop  for  any  reason  while  the  feed  continues.  The 


45°  slope  boot,  wheel  in  45°  slope  boot,  wheel  in 

High  Position.  Low  Position. 


FIG.  261. 

55°  slope  boot,  wheel  in 
High  Position. 


FIG.  262. 

55°  slope  boot,  wheel  in 
Low  Position. 


line  A — B  in  Figs.  260  and  262  shows  how  the  material  may  pile  in  the  two 
styles  of  boot  under  such  circumstances. 

Summary. — Boots  with  fronts  sloped  at  45°  (Figs.  259  and  260)  have  a 
low  chute,  save  some  depth  of  elevator  pit,  work  well  with  dry,  free-flowing 
materials,  but  not  so  well  with  sluggish  materials  unless  the  foot  wheel 
is  set  low  and  the  wheel  and  buckets  are  of  a  size  that  makes  the  sweep 
of  the  buckets  come  close  to  the  bottom  sheet.  Boots  with  fronts  sloped 
at  55°,  57^°  or  more  are  higher  in  front,  require  some  inches  more  of  depth 
in  the  boot  pit,  work  well  with  all  materials  fit  to  handle  in  centrifugal 
discharge  elevators,  but  require  free-flowing  substances  to  be  fed  with  some 
care,  so  as  not  to  swamp  the  foot  wheel  when  it  is  in  a  low  position  of  take- 
up  travel  (see  Figs.  261  and  262). 


288  ELEVATOR  BOOTS 

Fly-feed  or  Scoop-feed. — In  an  elevator  with  continuous  buckets  run 
at  comparatively  slow  speeds  it  is  possible  to  chute  the  material  directly 
into  the  buckets,  but  in  centrifugal  discharge  elevators,  where  the  buckets 
are  spaced  apart  on  a  belt  or  chain  and  travel  at  the  speeds  given  in  Table 
35  or  36,  there  is  little  or  no  gain  in  an  attempt  to  deliver  the  material 
directly  to  the  buckets,  the  so-called  "  fly-feed."  If  the  lip  of  a  chute  set 
for  "  fly-feed  "  is  at  or  below  the  level  of  the  foot  shaft  it  is  inoperative, 
because  the  material  will  be  thrown  out  of  the  buckets  by  centrifugal  force 
(see  p.  215)  and  will  drop  down  and  be  scooped  up  when  enough  has  accumu- 
lated under  and  in  front  of  the  foot  wheel.  If  the  chute  is  higher  and 
directs  the  stream  of  material  above  the  center  of  the  wheel  into  buckets 
moving  at  a  speed  of  5  to  10  feet  per  second,  only  a  part  of  it  is  caught, 
most  of  it  falls  down  into  the  boot,  and  some  may  be  splashed  and  scattered 
so  as  to  fall  on  the  top  of  the  foot  pulley.  Material  caught  between  the 
pulley  and  the  down  belt  wears  or  cuts  the  belt,  and  with  the  "  fly-feed  " 
the  other  side  of  the  belt  suffers  some  injury  from  the  direct  impact  of 
material  striking  it  between  the  buckets. 

The  best  feed  for  hard,  gritty,  lumpy  materials  handled  in  centrifugal 
discharge  elevators  is  the  "  scoop-feed  "  where  the  buckets  act  on  a  yielding 
mass  fed  in  on  the  sloping  front  of  a  boot,  or  where  the  delivery  is  such 
that  the  material  can  pile  to  form  its  own  boot.  The  slope  of  the  front 
of  the  boot  and  the  height  of  the  chute  with  reference  to  the  foot  wheel 
depend  on  the  nature  of  the  material,  whether  it  is  free-flowing  or  sluggish 
(see  p.  287). 

Feeding  into  Side  or  Back  of  Boot. — Since  buckets  in  centrifugal  dis- 
charge elevators  never  pick  up  material  below  or  behind  the  foot  wheel, 
feeding  into  the  boot  at  those  places  merely  adds  to  the  work  of  the  elevator 
belt  and  buckets  by  the  power  required  to  drag  the  material  over  the  inside 
surfaces  of  the  boot  or  over  a  bed  of  dead  material  from  the  place  of  feeding 
to  the  front  of  the  wheel  where  the  buckets  pick  up  their  load.  In  grain 
elevators  this  does  no  particular  harm  to  the  belt  or  buckets  because  the 
grain  moves  freely  and  causes  very  little  wear,  but  in  elevators  handling 
lumpy  or  abrasive  material  the  bottom  sheet  and  side  plates  of  the  boot, 
and  also  the  lips  of  the  buckets,  are  apt  to  be  worn  by  the  friction  of  the 
material  dragged  around  beneath  the  wheel.  A  more  serious  matter  is  the 
chance  that  pieces  may  wedge  fast  between  the  buckets  and  the  bottom 
sheet,  or  between  the  buckets  and  the  bed  of  dead  material  lying  beyond 
the  sweep  of  the  buckets,  with  the  result  that  buckets  are  torn  apart  or 
pulled  off  the  belt,  and  with  consequent  injury  to  the  belt  itself. 

It  is  often  convenient  to  feed  an  elevator  from  the  back  or  side  to  save 
depth  of  pit  and  height  and  length  of  feed  chutes.  When  the  material  is  in 
small  pieces  this  is  permissible,  but  it  is  dangerous  to  handle  hard  and 
lumpy  material  in  this  way. 

Where  the  foot  of  a  grain  elevator  is  lowered  into  a  cargo  of  grain  the 
foot  frame  of  the  "  marine  leg  "  must  be  open  at  sides  and  back  to  feed  to 
the  buckets.  Fig.  263  shows  such  an  open  frame;  when  it  is  in  operation 


SIZE  OF  FOOT  PULLEYS  289 

the  most  active  flow  of  material  is  at  the  back  where  the  buckets  go 
down. 

Size  of  Foot  Pulleys. — It  is  a'common  mistake  to  make  these  pulleys  too 
small.     The  object  may  Joe  to  saVe*  space,  or  to 
avoid  a  few  inches  greater   depth  of  pit,  or  to 
save  something  in  the  price  of  a  boot. 

So  far  as  the  belt  is  concerned,  the  general 
objection  to  a  small  pulley  is  that  it  tends  to 
separate  the  plies  of  fabric  in  a  built-up  belt  by 
stretching  or  breaking  the  bond  which  holds 
the  plies  of  fabric  together,  whether  that  bond 
is  stitching,  as  in  canvas  belts,  or  some  cement- 
ing compound,  as  in  rubber  or  balata  belts,  or 
the  binder  threads  in  a  solid- woven  belt.  In 
conveyor  practice,  foot  pulleys  have  seldom 
less  than  3  or  4  inches  of  diameter  per  ply 

of  belt.      Belt  elevators  are   generally  shorter   T 

J  FIG.  263. — Open  Boot  or  Foot 

between  centers  than  belt  conveyors  and  hence          Frame  of  Marine  Leg. 

the  belt  bends  over  the  pulleys  oftener  for  the 

same  belt  speed.  For  that  reason,  foot  pulleys  of  belt  elevators  should 
be  at  least  4  inches  in  diameter  for  each  ply  of  belt — that  is,  a  24-inch 
pulley  for  a  6-ply  belt.  If  the  elevator  is  short,  the  belt  bends  oftener, 
and  a  ratio  of  5  to  1  is  better  still,  to  prolong  the  life  of  the  belt  and  postpone 
the  day  when  the  belt  will  fail  by  separation  of  the  plies.  It  must  be  said, 
however,  that  most  elevator  belts  are  not  discarded  on  account  of  the 
internal  wear  which  causes  the  plies  to  separate;  some  belts  handling  clean, 
dry  substances  like  grain  may  die  of  old  age,  but  most  elevator  belts  suc- 
cumb to  external  injuries  which  have  no  connection  with  the  diameter  of 
the  pulleys  they  run  on. 

The  great  objection  to  a  small  foot  pulley  is  the  bad  pick-up.  For 
reasons  stated  in  Chapter  XV  and  shown  in  Figs.  204,  206  a  small  foot 
pulley  may  not  permit  the  buckets  to  pick  up  any  material  until  they  are 
on  the  straight  run  above  the  pulley  and  away  from  the  influence  of  centrif- 
ugal force.  When  that  happens,  the  buckets,  while  they  are  in  contact 
with  the  foot  wheel,  do  nothing  but  stir  up  material  uselessly,  wear  them- 
selves out  and  perhaps  injure  the  belt. 

The  larger  the  foot  wheel  in  comparison  with  the  head  wheel  of  a  cen- 
trifugal discharge  elevator,  the  less  the  influence  of  centrifugal  force  in  the 
boot,  the  lower  the  buckets  pick  up  their  load,  and  the  less  the  energy  wasted 
in  the  boot. 

Large  foot  pulleys  are  better  than  small  ones  in  another  respect;  they 
support  the  buckets  better  when  the  latter  pick  up  their  load.  Fig.  264 
shows,  to  scale,  a  bucket  with  6-inch  projection  on  a  6-ply  belt  running 
on  a  15-  or  a  27-inch  pulley.  Since  the  bolt  fastening  is  not  rigid,  the  bucket 
moves  in  the  direction  of  the  arrow  when  it  meets  some  resistance  from  the 
material,  thus  exerting  a  pull  on  the  bolts  until  the  bucket  finds  a  backing 


290 


ELEVATOR  BOOTS 


against  the  belt  at  some  point  A.  The  larger  the  pulley,  the  less  the  bucket 
will  move  and  the  smaller  will  be  the  pull  on  the  bucket  bolts.  It  will  also 
gap  away  from  the  belt  less  at  B  and  bits  of  material  will  not  be  so  likely  to 
catch  and  stick  there  and  injure  the  belt. 

Material  Catching  between  Belt  and  Foot  Pulley. — More  elevator  belts 
are  injured  from  this  cause  than  from  any  other.  The  pieces  of  material 
which  cause  the  trouble  may  have  been  spilled  from  the  buckets  on  the 
vertical  run  or  on  the  head  wheel;  or  lumps  may  fall  from  the  head  chute 
on  a  rebound,  or  when  the  material  backs  up  in  the  chute  from  a  choke  or 
when  the  bin  it  supplies  is  full.  When  the  feed  chute  is  too  high  with  refer- 
ence to  the  foot  wheel,  or  when  it  is  set  for  "  fly-feed,"  this  trouble  is  more 


FIG.  264. — Better  Support  of  Bucket 
on  Foot  Wheel  of  Large  Diameter. 


FIG.  265. — Deflector  for  Spill  on  Return 
Run  of  Elevator. 


likely  to  occur  than  when  the  chute  delivers  to  a  sloped-front  boot  of  proper 
design. 

Guards  placed  close  over  the  pulley  do  not  cure  the  trouble  altogether. 
If  placed  so  close  to  the  pulley  as  to  shed  falling  pieces,  they  may  serve  to 
confine  material  which  has  gotten  through  the  clearance  space  which 
must  be  left  between  the  guard  and  the  belt,  and  thus  do  more  harm  than 
good.  If  the  elevator  is  inclined  instead  of  vertical,  spill  from  the  head  is 
less  likely  to  fall  on  the  foot  pulley,  especially  if  the  casing  is  made,  as  in 
Fig.  257,  with  a  vertical  face  on  the  descending  side. 

In  some  inclined  elevators  handling  large  pieces  of  stone,  guards  or 
shields  have  been  used  with  success  to  deflect  from  the  foot  pulley  any 
pieces  of  stone  which  may  fall  or  roll  down  along  the  inside  face  of  the 
descending  belt.  Fig.  265  shows  such  a  device;  it  consists  of  a  heavy 
plank  set  diagonally  across  the  elevator  above  the  foot  pulley  and  provided 


ELEVATORS  WITH  NO  FOOT  PULLEY 


291 


C 


on  its  lower  edge  with  several  thicknesses  of  old  belting  which  project 

far  enough  to  keep  close  to  the  elevator  belt  and  yet  yield  when  the  belt 

vibrates  or  sways,  as  it  always  does^ 

Devices  like  this  need  the  intelligent  interest  of  the  men  in  active  charge 

to  keep  them  in  working  order.     The  plank  may  need  adjusting  from  time 

to  time,  or  the  strips  of  belting  may  have  to  be  replaced  when  worn.     With 

such  attention,  a  guard,  like  the  one  shown,  may  prevent  serious  injury 

to  the  belt  and  may  pay  for  itself  many  times  over  in  the  longer  life  of  the 

belt;  without  such  attention,  it  may  be  discarded  as  a  failure. 

Elevators  with  no  Foot  Pulley. — The  chances  of  injuring  the  belt  would 

be  fewer  if  belt  elevators  could  be  run  without  foot 

pulleys.     This  has  been  done  in  the  works  of  a  copper 

company  in  Arizona.     Up  to  1920,  six   or   eight    ele- 
vators had  been  put  in  at  this  plant,  under  the  Cole 

patent  of  March  2,  1920  (Fig.  266),  which  covers  the 

use  of  a  belt  elevator  without  a  foot  pulley  but  with  a 

normally  slack  belt  guided  by  a  pulley  on  the  rising 

side   above   the  feed  point.     Some  of  these  elevators 

had  24-inch  belts  about   10-ply  with  16-inch   buckets 

set   staggered.      "  When   running    at   the   speed  for  a 

proper  dumping  effect  for  the   buckets  the  lower   end 

of   the  belt  loop  would   take  a  form   almost  the  same 

as  that  of  the  boot  pulley  and  would  take  up  the  feed 

as  well  as  if  the  usual  boot  pulley  were  used.     The 

snub  pulley  would  only  come  into  play  when  an  excess 

of  feed  was  fed  to  the  machine.     There  was  no  strain 

on  the  belt  other  than  that  of  carrying  the  load;   no 

sand  or  quartz  particles  were  forced  into  the  cover  of 

the  belt,  the  latter  being  clean  all  the  time."  l 

There  are  many  elevators  in  which  the  load  is  so 

heavy  that  take-up  tension  must  be  added  in  order  to  get  sufficient  driving 

effect  (see  p.  299).     In  such  cases,  the  foot  pulley  is  a  necessity. 

Special   Foot   Pulleys. — Several  forms   of 

pulley  have  been  used  to  lessen  the  risk  of 
injuring  the  belt.  The  Boss  pulley  shown  in 
Fig.  267,  presents  less  surface  to  the  belt,  and 
if  the  material  is  fine  and  dry  it  will  be  shed 
to  each  side  of  the  belt  by  the  conical  sur-. 
faces  in  the  pulley.  Flanged  pulleys  in  two 
sections  have  been  used  (Fig.  268) ;  they  offer 
less  surface  to  the  belt,  but  since  the  pulley 
has  no  crown,  flanges  are  necessary  to  guide 
the  belt.  The  flanges  are  bad  because  the 

edges  of  the  belt  tend  to  ride  up  on  them  and  are  worn,  and  the  wheels 

are  likely  to  act  as  a  trap  for  material  rather  than  a  relief  for  the  belt. 
1  Communicated  to  the  author  by  Mr.  David  Cole. 


J?'  266.  —  Crushed 
Ore  Elevator  with  No 
Foot  Pulley. 


FIG.  267.— Foot  Pulley  with  No 
Rim. 


292 


ELEVATOR  BOOTS 


Neither  of  these  devices  is  of  use  when  the  material  handled  is  in  pieces 
that  will  wedge  in  the  pulley.     A  piece  of  sharp  stone  wedged  between  the 

halves  of  the  flanged  pulley 
or  between  the  arms  or  vanes 
of  the  Boss  pulley  may  go 
around  many  times  and  hurt 
the  belt  in  many  places, 
while  the  same  piece  might 
go  once  around  an  ordinary 
pulley  and  then  fall  off. 

It  is  possible  that  foot 
pulleys  for  thick  and  heavy 
belts  on  elevators  handling 
ores  and  stone  might  be 
made  with  pneumatic  or 
cushion  rims  that  would  be 


FIG.  268. — Double  Flanged  Foot  Pulley. 


more  yielding  than  the  belt  and  still  be  rigid  enough  to  guide  the  belt  and 
apply  tension  to  it. 

The  problem  is  a  serious  one,  and  one  that  is  hard  to  solve.  Men  in  the 
business  have  seen  10-ply  belts  cut  clear  through  by  stone  jammed  against 
the  foot  pulley;  the  force  that  will  do  this  is  hard  to  control  by  mechanical 
means.  At  present  it  is  not  attempted;  the  burden  is  put  on  the  belt 
manufacturers,  and  they  are  making  belts  thicker  and  heavier,  with  outer 
covers  and  internal  cushions  of  rubber  to  resist  the  blows  and  the  pressure. 

Ordinary  Foot  Pulleys  for  elevators  handling  coal  and  other  materials 
which  are  not  too  abrasive  are  generally  made  in  "  double-belt  "  weight 
which  for  the  usual  range  of  diameters,  from  15  to  30  inches  and  faces  6  to 
18  inches,  means  that  the  edge  of  the  rim  is  \  to  -f$  inch  thick  at  the  edge  and 
f  to  \  inch  thick  in  the  center.  The  crown  is  usually  standard — that  is, 
|  inch  on  the  diameter  per  foot  of  face.  The  face  measures  f  to  2  inches 
wider  than  the  belt  for  the  sizes  used  in  elevator  boots. 

In  handling  sand  and  ores,  the  stir  of  material  in  the  boot  and  the  fine 
stuff  adhering  to  the  belt  combine  to  wear  out  the  rims  of  ordinary  foot 
pulleys.  For  this  service  it  is  economical  to  order  pulleys  with  rims  thicker 
than  standard,  and  with  heavy  arms,  or  with  plate  centers  instead  of  arms. 

Fastening  Foot  Pulleys  to  Shafts. — On  this  subject,  see  page  298. 

Amount  of  Take-up  Travel. — Take-ups  for  belt  conveyors  are  often  made 
with  3  feet  or  more  of  travel,  so  that  6  feet  or  more  of  belt  stretch  can  be 
removed  without  cutting  and  resplicing  the  belt.  Elevator  belts  are 
generally  shorter  than  conveyor  belts  and  the  stretch  is  less,  but  aside  from 
that,  the  range  of  travel  of  the  foot  shaft  in  a  take-up  boot  must  be  limited 
between  positions  at  which  the  buckets  will  pick  up  material  properly  and 
at  which  the  feed  chute  will  neither  be  choked  nor  yet  swamp  the  foot 
wheel  (see  p.  287). 

This  circumstance  limits  the  take-up  travel  in  grain  boots  to  12  or  15 
inches  and  in  other  belt  elevators  to  6  or  8  inches.  In  chain  elevators  the 


LUBRICATION  OF  BOOT  BEARINGS  293 

take-up  travel  should  be  at  least  enough  to  permit  the  removal  of  one  pitch 
of  chain,  if  the  links  are  all  alike*  of  two  pitches  if  the  links  are  alternately 
inside  and  outside,  as  in  some  sfeel  chains;  and  in  continuous  bucket 
elevators,  at  least  enough  to  remove  one  bucket. 

Lubrication  of  Boot  Bearings. — Although  oil  is  generally  used  for  the 
bearings  of  grain  boots  (see  p.  297),  grease  is  preferable  for  most  elevators 
handling  coal,  minerals,  ores  and  rough  materials.  It  is  better  suited  to  the 
cheap  and  simple  bearings  used  in  such  machines,  and  in  many  cases  it 
keeps  dirt  out  of  the  bearings  by  forming  a  collar  or  ring  where  it  squeezes 
out  of  the  end.  The  best  way  to  apply  grease  is  to  put  the  grease  cup 
directly  on  the  bearing  (see  Fig.  254  or  Fig.  256);  if  the  pit  is  deep  or  if 
one  side  of  the  boot  is  inaccessible,  a  pipe  may  be  used  to  lead  the  grease  to 


FIG.  269. — Automatic  Take-up  Boot  with  Grease  Pockets  on  the  Bearing^. 

the  bearing.  There  is  always  some  uncertainty  about  lubricating  in  this 
way;  if  the  pipe  is  long,  or  is  bent,  or  has  elbows  in  it,  the  grease  may  clog 
in  it  in  spite  of  screwing  down  the  cap  of  the  grease  cup.  Turning  the  cap 
may  merely  compress  air  in  the  pipe,  or  if  the  cap  is  small,  it  may  turn  so 
hard  that  with  some  classes  of  labor  it  will  be  neglected. 

To  make  sure  of  lubrication  in  spite  of  occasional  neglect,  boots  are 
made  (Fig.  269)  with  large  grease  pockets  cast  on  the  bearings.  The  mass 
of  grease  rests  directly  on  the  shaft  and  feeds  to  it  by  gravity.  Other 
boots  have  bearings  made  of  hard  wood  impregnated  with  oil;  these  bearings 
require  no  lubricant,  they  are  comparatively  cheap  and,  when  worn,  they 
are  thrown  away.  Fig.  270  shows  an  arrangement  which  has  been  used  in 
the  Western  mining  country.  The  boot  shaft  is  a  hollow  brass  shaft 
which  contains  a  supply  of  oil;  wicks  feed  oil  to  the  bore  of  the  foot  pulley 
which  runs  loose  on  the  shaft ;  the  shaft  itself  does  not  revolve.  In  elevators 


294 


ELEVATOR  BOOTS 


handling  gritty  ores,  the  pulley  side  of  the  belt  may  be  worn  off  if  the  foot 
pulley  does  not  revolve  freely.  The  pulley  in  an  ordinary  boot  may  stick 
if  the  two  take-up  screws  are  not  adjusted  alike  or  if  the  two  bearings  bind 
the  shaft  because  of  dirt  or  lack  of  lubricant.  When  the  pulley  is  loose  on 
the  shaft,  as  in  Fig.  270,  it  is  more  certain  to  turn;  there  is  less  weight  to 
be  revolved  and  the  turning  of  the  pulley  is  not  affected  by  the  way  the 
take-ups  are  adjusted. 

In  some  elevators  no  attempt  is  made  to  lubricate  the  foot  bearings. 
In  hot-clinker  elevators  in  cement  mills  the  foot  bearings  are  hard  to  get  at, 
being  in  a  deep  pit  where  the  heat  is  intense.  It  is  good  practice  here  to 
use  chilled  iron  bearings  and  run  them  until  they  are  worn  out.  It  is 
more  economical  to  do  this  than  to  use  better  bearings  and  then  pay  for 
oil,  attendance  and  maintenance.  A  bearing  which  is  not  lubricated  may 


FIG.  270.— Loose  Foot  Pulley  on  Hollow  Shaft  with  Internal  Lubrication. 

screech  and  get  hot,  but  these  faults  are  not.  serious  at  the  foot  of  a  clinker 
elevator.  These  elevators  are  chain  machines,  but  the  same  principle 
also  applies  to  some  belt  elevators.  On  this  point,  see  page  285. 

Grain  Elevator  Boots. — Old-time  boots  were  of  wood,  made  either  as  a 
prolongation  of  a  wooden  casing  or  pair  of  legs,  or  as  a  separate  box  on  which 
the  casing  was  mounted.  The  latter  construction  was  more  expensive,  but 
the  bearings  were  often  mounted  in  a  better  way,  the  interior  was  more 
accessible  and  the  boot  was  more  easily  cleaned.  Wood  boots  are  still  used 
in  some  places;  but  they  are  subject  to  decay  in  damp  pits,  they  get  out  of 
shape  under  the  weight  of  high  casings,  and  there  is  always  the  risk  of  a 
fire  starting  in  a  wood  boot  from  a  combination  of  oil-soaked  wood  and  the 
heat  from  a  bearing  which  has  not  been  lubricated  properly. 

Modern  grain  boots  consist  either  of  the  base  portion  of  a  steel  casing 
or  of  a  structure  of  cast-iron  and  steel  plate  on  which  a  steel  or  wood  casing 
is  mounted.  The  former  construction  is  often  used  in  modern  elevators 


CAST-IRON  BOOTS 


295 


where  the  legs  are  very  high,  and  where,  on  account  of  a  large  head  wheel, 

the  lower  sections  of  the  down  l^eg"  approach  the  foot  at  a  decided  slant. 

Fig.  271  shows  such  a  steel-plate  b^ot  with  a  30-inch  diameter  foot  pulley 

for  a  40-inch  belt.     It  is  "built  as 

part    of    the    casing  with    j^-inch 

plate,     2-inch    angles    and    f-inch 

bolts  and  rivets  4-inch  pitch.    Two 

3%-inch  removable  slide  plates  give 

access  to  the  inside  of  the  boot, 

front  and  back.     The  shaft  is  2^& 

inches  with   15-inch   travel.     The 

elevator    is    196   feet     center     to 

center.    The  boot  bearings  slide  up 

and    down   in    a    cast-iron    frame 

bolted  to  the  boot  sides,  and  carry 

a  slide  plate  which  closes  the  slot 

on    each    side    of    the    boot.      A 

weighted  frame  mounted  above  the  shaft  provides  an   automatic  take-up 

for  slack  a"nd  keeps  a  tension  on  the  belt. 

Cast-iron  Boots. — Various  styles  of  grain  boots  are  listed  by  manu- 


FIG.  271. — Foot  of  40-inch  Receiving  Leg. 
Public  Grain  Elevator,  New  Orleans.  (Ford, 
Bacon  &  Davis,  Engrs.) 


FIG.  272. — Cast-iron  Grain  Boot  with  Removable  Bottom  Plates.     (Used  with  Wooden 

Legs.) 

facturers.  Generally  they  have  cast-iron  sides  joined  by  cast-iron  or  steel 
plates  curved  to  form  the  bottom  of  the  boot.  In  the  best  designs,  por- 
tions of  the  bottom  plates  are  removable  (Fig.  272)  to  give  access  to  the 


296 


ELEVATOR  BOOTS 


inside  for  cleaning  or  removing  obstructions;  sometimes  only  small  clean- 
out  doors  in  the  side  plates  are  provided,  but  these  are  too  small  to  do  much 
good  when  the  boot  chokes.  At  such  a  time,  the  grain  is  piled  higher  than 
the  shaft  and  it  is  better  to  get  at  the  trouble  quickly  by  removing  a  section 
of  the  bottom  so  that  a  shovel  can  be  used,  and,  if  necessary,  damaged 
buckets  can  be  taken  off  the  belt. 

Fig.  273  shows  a  heavy  cast-iron  boot  for  a  large  grain  elevator  with  a 
24-inch  pulley  and  11  inches  of  adjustment.  The  bearings  (Fig.  274)  are 
closed  at  one  end,  and  the  opening  at  the  other  for  the  2j^-inch  shaft  is 
sealed  against  the  entrance  of  dust  and  dirt  and  against  the  leakage  of  oil 
by  a  felt  washer  and  a  packing  ring.  It  carries  a  supply  of  oil  in  the  base  of 
the  casting,  enough  for  several  weeks'  run.  A  loose  brass  oil-ring  delivers 


M.^  Handle  to 
)V  Tighten  DttH 


Set  Boot  1  Above  Floor  Level  **    bteel  • 

•^  »      »    3"  >•         ,,        »      when  Placed  in  Boot  Tank 


FIG.  273. — Heavy  Cast-iron  Grain  Boot  used  with  Steel  Casing. 
(Witherspoon-Englar  Co.) 

oil  to  the  shaft  and  a  hinged  cover  permits  the  attendant  to  see  whether 
the  ring  turns  and  the  oil  reaches  the  shaft.  The  trunnions  or  pivots  of  the 
bearing  are  carried  in  a  slide  casting,  so  that  the  shaft  can  be  leveled  and  the 
belt  made  to  run  straight  on  the  pulley  independent  of  the  setting  of  the 
boot.  The  slide  casting  is  pinned  to  the  adjusting  screw  and  travels  with 
it,  the  screw  being  moved  by  a  handwheel  which  acts  as  a  nut.  The  screw 
does  not  turn. 

Lubrication  of  Grain  Boots. — In  cheaper  boots  the  adjusting  screw 
turns,  is  necked  at  the  lower  end  and  has  a  loose  connection  with  the  bear- 
ing itself,  and  in  some  of  them  the  oil  is  fed  to  the  bearing  through  the  screw 
itself,  which  is  then  made  of  heavy  pipe  or  hydraulic  tubing.  Experience 
with  this  method  of  oiling  is  not  altogether  satisfactory;  dirt  gets  into  the 
loose  connection  at  the  lower  end  of  the  screw  and  plugs  the  oil  hole  shut. 
Boots  are  often  placed  in  deep  and  narrow  pits  and  it  may  be  desirable 


LUBRICATION  OF  GRAIN  BOOTS 


297 


to  oil  the  bearings  from  the  floor  level,  but  in  such  cases  it  is  better  to  use 
separate  oil  pipes  screwed  tigh^  hito  the  bearings  and  not  oil  through 
the  take-up  screws. 

Oil  is  generally  used  fer  the  bearings  of  grain  boots,  on  account  of  the 
high  speed  of  the  shaft,  often  100  r.p.m.,  and  for  cleanliness.  The  objec- 
tion to  grease  lubrication  is  that  the  dirty  collar  of  grease  which  accumulates 
at  the  ends  of  the  bearings  may  fall  off  into  the  grain  and  spoil  it  for  flour- 
milling. 

In  some  ways  it  is  better  that  the  attendant  should  get  down  into  the 
pit  to  oil  the  bearings;  he  can  then  see  and  feel  the  bearings  and  make  an 
inspection  of  the  boot.  It  is  a  common  experience  that  boot  bearings  are 
apt  to  be  neglected;  then  if  the  shaft  should  seize  tight  in  a  hot  bearing, 


FIG.  274. — Self-oiling  Trunnion  Bearing  for  High-speed  Grain  Elevator  Boot  Shown  in 

Fig.  273. 

there  is  danger  that  the  pulley  may  stand  still  and  rub  off  the  inner  plies  of 
the  belt,  or  if  the  pulley  is  fastened  only  by  set  screws,  it  may  turn  while  the 
set  screws  gouge  grooves  in  the  stationary  shaft,  or  it  may  shift  end  ways 
on  the  shaft  until  its  rim  cuts  through  the  side  of  the  boot.  These  mishaps 
sometimes  cause  expensive  shut-downs  and  then  costly  repairs.  In  the 
design  of  important  grain  elevators  it  is  well  to  provide  for  good  lubrication 
by  using  well-made  self-oiling  bearings,  to  make  the  pit  large  enough  for 
access  to  both  sides  and  both  ends  of  the  boot,  and  to  keep  the  bearings 
outside  the  boot  where  they  can  be  seen  and  felt.  In  the  large  elevator 
shown  in  Fig.  271  the  foot  shaft  with  its  pulley,  slides  and  automatic  tension 
device  weighed  over  2200  pounds;  a  load  of  about  1100  pounds  on  each 
shaft  bearing  at  about  100  r.p.m.  represents  a  duty  important  enough  to 


298  ELEVATOR  BOOTS 

deserve  good  bearings,  thorough  lubrication  and  regular  inspection.  As  a 
precaution  against  heating,  the  foot  bearings  of  elevators,  as  well  as  other 
bearings,  are  in  some  cases  fitted  with  fusible  metal  plugs  which  make 
electrical  contact  and  sound  an  alarm  when  the  temperature  of  the  bearing 
goes  over  165°  F.  or  some  other  established  temperature. 

Pulleys  in  Grain  Boots  are  always  made  with  a  crown  face  and  of  the 
weight  known  in  the  trade  as  "  double-belt."  In  small  elevators  it  is  suf- 
ficient to  hold  the  pulley  in  place  on  the  shaft  by  two  set  screws,  but  it  is 
always  an  advantage,  and  in  important  work  it  is  very  desirable,  to  hold 
the  pulley  more  securely.  It  is  a  common  complaint  that,  in  conveying 
and  elevating  machinery,  set-screwed  wheels  will  not  stay  in  place,  but 
shift  on  the  shaft.  The  reason  is  that  commercial  shafting  varies  in  diam- 
eter from  its  nominal  size;  it  is  seldom  oversize  but  often  .003  or  .004  inch 
undersize.  Pulleys  in  the  trade  are  bored  and  reamed  a  few  thousandths 
oversize  to  make  sure  of  their  going  on  commercial  shafting;  the  result 
is  that  when  a  set-screwed  pulley  with  an  oversize  bore  goes  on  an  under- 
size shaft  with  perhaps  .005  to  .01  inch  clearance,  it  is  very  apt  to  shift, 
especially  if  the  face  is  wide  and  the  hub  relatively  short.  Some  men  in 
charge  of  grain  elevators  (and  other  elevators)  always  "  spot  "  the  shaft, 
that  is,  drill  shallow  recesses  in  it  to  receive  the  points  of  the  set  screws; 
some  use  long  set  screws  with  lock  nuts  to  keep  them  tight  in  the  pulley 
hub;  some  keep  the  pulley  in  place  by  fastening  collars  with  set  screws  to 
the  shaft  on  each  side  of  the  pulley  hub.  A  better  way  for  pulleys  and 
shafts  of  commercial  grade  is  to  key  the  pulley  to  the  shaft  with  a  fitted 
key  and  put  two  set  screws  over  the  key.  A  still  better  way,  although 
it  is  seldom  used  for  foot  shafts,  is  to  turn  the  shaft  to  an  exact  diameter, 
bore  the  wheel  a  few  thousandths  small  and  then  press  or  drive  it  on. 

Pulleys  wider  than  20-inch  face  should  have  double  arms. 

Pulleys  for  large  elevators  are  generally  made  with  closed  ends,  usually 
by  fastening  on  steel-plate  disks,  so  that  the  grain  is  kept  out  of  the  pulley 
and  the  arms  do  not  add  to  the  work  of  the  elevator  belt  by  stirring  up  the 
grain. 

Automatic  Boot  Take-ups  may  be  used  (1)  as  a  convenience  to  avoid 
attention  to  take-up  screws;  (2)  to  maintain  driving  contact  on  the  foot 
pulley  or  sprocket  wheel  in  those  exceptional  cases  where  an  elevator  is 
driven  at  the  foot  or  where  power  is  taken  from  the  foot  shaft ;  (3)  in  chain 
elevators,  to  prevent  loose  chain  from  climbing  up  on  the  teeth  of  the  foot 
wheel;  (4)  in  belt  elevators,  to  maintain  a  tension  T2  in  the  down  belt  by 
applying  a  load  to  it  which  will  act  regardless  of  the  normal  stretch  in  the 
operation  of  the  belt. 

The  last  item  is  the  most  important,  and  it  is  the  one  to  be  considered 
here.  For  a  discussion  of  it,  see  page  270.  It  is  evident  that  if  the  load  is 
light  and  the  driving  conditions  at  the  head  of  the  elevator  are  favorable 
there  is  little  or  no  need  for  artificial  tension  in  the  belt;  but  if  the  load  is 
heavy  and  if  the  belt  is  dirty,  wet,  or  works  in  an  atmosphere  of  dust,  the 
coefficient  of  belt  contact  falls  off  and  then  there  is  need  of  artificial  tension 


ARTIFICIAL  TENSION  IN  VERTICAL  ELEVATOR  BELTS       299 


T 

to  maintain  the  proper  ratio  of  — -..    There  is  also  need  for  artificial  tension 

if  the  belt  is  heavily  loaded  even  though  clean;  that  condition,  or  an  over- 
load in  the  boot,  has  the  effect  of  increasing  TI,  and  unless  T2  is  great  enough 
the  belt  will  slow  down  and  slip. 

The  great  practical  advantage  of  a  weighted  take-up  on  a  belt  elevator 
is  that  a  steady  artificial  tension  can  be  applied  to  the  down  belt  which 
will  keep  T2  high  enough  to  prevent  slip  and  avoid  a  choke  in  the  elevator. 
On  the  effect  of  belt  slip,  see  page  277. 

Artificial  Tension  in  Vertical  Elevator  Belts. — Table  56  has  been  pre- 
pared to  show  what  artificial  tension  is  necessary  in  vertical  elevators 
for  various  conditions  of  drive  and  for  various  values  of  /,  the  coefficient  of 
belt  contact.  For  instance,  an  elevator  handling  a  clean,  sized  material 
has  a  belt  that  weighs  2.3  pounds  per  foot;  empty  buckets  weigh  4.3  pounds 
per  foot  and  the  material  in  the  buckets  3.5  pounds  per  foot.  Then  the 

V      2  S -4-4  3-1-3  5 

ratio  —  =— : —  =  1.6   and   from   Table   56  it  is  evident  that  no 

TI         2.3+4.3 

belt  tension  need  be  applied  at  the  boot  for  any  kind  of  drive.     It  is  not 

TABLE  56.— ARTIFICIAL  TENSION  FOR  VERTICAL   BELT  ELEVATORS 

TI  =  weight  of  loaded  belt  and  buckets,  plus  pull  to  dig. 
T2  =  weight  of  empty  belt  and  buckets. 

Tension  to  be  applied  at  boot  to  maintain  driving  contact  at  head-pulley.  Figures 
are  percentages  of  T2  to  be  added  to  TI  and  to  T2. 


1 

2 

3 

4 

5 

6 

7 

Rubber-Covered  Pulleys 

Plain  Iron  Pulleys 

Ratios 

of 

T! 

£  =  3.00. 

—  1  =  2.33. 

—  '  =  1.87. 

—  =2  19. 

—  •  =  !  87. 

—  =  1  87 

T2 

T2 

T2 

T2 

T2 

T2 

T2 

Clean. 

Dusty. 

Wet. 

Clean. 

Dusty. 

Wet. 

/=.35 

/=.27 

/=  .20 

/=.25 

/=.20 

/=.20 

1.8 

0 

0 

0 

0 

0 

0 

1.9 

0 

0 

3 

0 

3 

3 

2.0 

0 

0 

15 

0 

15 

15 

2.1 

0 

0 

26 

0 

26 

26 

2.2 

0 

0 

37 

1 

37 

37 

2.3 

0 

0 

49 

9 

49 

49 

2.4 

0 

5 

60 

17 

60 

60 

2.5 

0 

13 

72 

26 

72 

72 

2.6 

0 

20 

84 

34 

84 

84 

2.7 

0 

28 

95 

43 

95 

95 

2.8 

0 

35 

107 

51 

107 

107 

2.9 

0 

43 

118 

60 

118 

118 

3.0 

0 

50 

130 

68 

130 

130 

3.1 

5 

58 

141 

77 

141 

141 

3.2 

10 

65 

153 

85 

153 

153 

3.3 

15 

73 

164 

93 

164 

164 

3.4 

20 

80 

175 

102 

175 

175 

3.5 

25 

88 

187 

110 

187 

187 

300  ELEVATOR  BOOTS 

necessary  to  lag  the  head  pulley,  and  an  iron  pulley  might  be  expected  to 
drive  the  belt  even  though  the  surfaces  in  contact  were  wet,  provided  the 
work  of  picking  up  material  from  the  boot  were  not  great.  If  the  buckets 

T 
carried  a  heavier  material,  or  if  the  pick-up  were  harder,  the  ratio  —  might 

Tt 

rise  to  2.0  and  then  it  would  be  necessary,  for  wet  conditions,  to  load  the 
down  belt  (and  necessarily  the  up  belt)  at  the  boot  with  about  15  per  cent 
of  the  dead  weight  of  the  down  run.  That  is,  if  the  empty  belt  and  buckets 
on  the  down  side  weighed  400  pounds,  then  the  added  load  at  the  boot 
(considering  both  runs  of  belt)  would  be  400  X.  15x2  =  120  pounds. 

When  the  buckets  must  dig  their  load  from  the  boot  the  pull  in  the  up 
belt  is  more  than  the  weight  of  the  belt  and  loaded  buckets  by  the  pull 
required  to  dig.  In  grain  elevators  the  buckets,  and  often  the  belt,  are 
relatively  light;  this  factor,  on  the  one  hand,  and  on  the  other  the  con- 

T 
siderable  pull  required  to  dig,  combine  to  raise  the  ratio  of  —  to  2.5  or 

TZ 

more.  In  the  example  quoted  in  Chapter  XX  the  ratio  was  2.63,  and 
from  Table  56  it  is  evident  that  under  the  operating  conditions  —  a  rubber- 
covered  head  pulley  working  in  a  dust  —  it  would  be  necessary  to  apply 
to  the  belt  in  the  boot  a  load  of  22.5  per  cent  X  2  =  45  per  cent  of  the  weight 
of  the  down  belt  with  its  buckets,  or  2700X.45  =  1215  pounds. 

Varying  the  Boot  Tension  with  the  Load.  —  When  the  operating  capacity 
of  a  grain  elevator  is  based  upon  not  more  than  80  per  cent  of  the  level-full 
capacity  of  the  buckets,  as  rated  in  the  catalogues  of  manufacturers,  there  is 
generally  margin  enough  to  provide  for  ordinary  contingencies  of  feed;  but 
if  the  feed  is  irregular  and  subject  to  fluctuations  beyond  the  normal  rate  of 
loading,  or  if  the  capacity  of  the  elevator  is  to  be  forced  at  times  beyond 
80  per  cent  of  the  rated  capacity  of  the  buckets,  then  provision  should 
be  made  to  apply  extra  belt  tension  at  the  boot,  if  necessary,  so  that  the 

T 

ratio  of  —  does  not  become  too  large  for  the  driving  conditions  at  the  head 
T2 

of  the  elevator. 

Illustration.  —  In  the  elevator,  the  boot  of  which  is  shown  in  Fig.  271, 
the  empty  belt  and  buckets  on  the  down  leg  weighed  about  4200  pounds 
and  for  a  capacity  of  20,000  bushels  per  hour  the  loaded  belt  on  the  up  leg 
weighed  about  10,000  pounds;  allowing  800  pounds  for  the  digging  and 

10  800 
friction  in  the  boot,  the  ratio  of  belt  tensions  is  —  -  -  =2.57,  and  from  inter- 

polation in  Table  56,  Column  3,  the  total  weight  to  be  applied  to  the  boot  is 
4200X.  179x2  =  1500  pounds.  For  a  capacity  of  22,500  bushels  per  hour 

11  500 
the  ratio  is  —  '-  -  =  2.74  and  the  weight  required  is  4200  X.  308x2  =2600 


pounds.     For  the  maximum  rating  of  the  elevator,   25.000  bushels  per 

12  200 

hour,  the  ratio  is  —  -  -  =2.9  and   the  weight  required  is  4200  X.  43x2  = 
4200 


VARIETIES  OF  AUTOMATIC  BOOT  TAKE-UPS 


301 


3600  pounds.  These  values  are,  of  course,  based  on  the  assumed  coefficients 
of  belt  contact  as  stated  in  Tatye*56,  but  they  agree  quite  well  with  the 
best  practice  in  grain-elevator  design  and  operation. 

On  the  permissible  unit  stresses  in  elevator  belts,  see  page  274. 

Varieties  of  Automatic  Boot  Take-ups. — A  simple  way  is  to  make  the 
foot  pulley  heavy  enough,  or  add  weights  to  the  boot  shaft,  to  take  up 
the  slack  or  maintain  the  proper  tension  on 
the  belt.  In  some  belt  elevators  with  36-inch 
10-ply  belts,  used  by  a  Western  copper- 
mining  company,  the  foot  pulleys  are  42 
inches  in  diameter  with  rims  2\  inches  thick. 
The  foot  bearings  slide  in  guides,  and  no 
take-up  screws  are  used.  An  old  device  is 
a  pair  of  levers,  one  on  each  side  of  the  boot, 
pivoted  at  one  end,  weighted  at  the  other  end 
and  with  an  intermediate  link  bearing  down 
on  top  of  the  boot  bearing.  One  arrange- 
ment is  shown  in  Fig.  275.  Several  patents 
of  no  worth  have  been  issued  on  arrange- 
ments where  the  whole  boot  is  hanging  on  the 
loop  of  belt  and  is  guided  by  sleeves  or  tracks 
on  the  lower  part  of  the  elevator  casing.  A 
few  elevators  have  been  built  where  the 
whole  weight  of  the  boot  is  carried  on  a 
pivoted  arm  so  as  to  maintain  a  tension  on 
the  elevator  belt  or  chain,  and  since  the  wheel 
does  not  travel  within  the  boot,  a  fixed  dis-  FIG.  275.— Weighted  Lever  Device 
tance  is  preserved  between  the  sweep  of  the  for  Automatic  Take-up, 

buckets  and  the  bottom  of  the  boot.     This  is 

an  advantage  in  handling  lumpy  materials  and  materials  like  fertilizers, 
which  form  a  hard,  dense  crust  beyond  the  sweep  of  the  buckets,  but  it 
is  of  no  value  in  handling  grain  or  similar  substances  (see  Fig.  258). 

Edmond  Take-up. — A  practical  device  used  on  many  large  grain  eleva- 
tors is  the  Edmond  automatic  take-up  (Edmond-Norell  patent  of  1911). 
It  consists  of  a  weighted  frame,  like  that  shown  in  Fig.  271,  for  maintaining 
the  tension  on  the  belt,  plus  means  for  independently  moving  the  foot 
bearings  in  the  frame  so  as  to  adjust  the  level  of  the  shaft  and  cause  the 
belt  to  run  true  on  the  foot  pulley.  In  practice,  the  lead  of  the  down 
belt  on  to  the  foot  pulley  is  also  controlled  by  adjusting  the  deflector  pulley 
which  in  large  elevators  is  placed  in  the  down  leg  where  it  leaves  the  vertical 
to  slant  to  the  boot.  A  very  slight  deviation  of  this  pulley  from  true  level 
will  train  the  belt  one  way  or  the  other  on  the  foot  pulley. 

Fig.  269  shows  a  belt  elevator  boot  in  which  the  belt  tension  is  main- 
tained by  a  weighted  lever  device. 

Chokes  in  Grain-elevator  Boots  are  due  to  various  causes: 

1.  Elevating  capacity  of  the  buckets  is  too  small  for  the  feed. 


302  ELEVATOR  BOOTS 

2.  Bins  become  full ;  grain  backs  up  in  head  chute,  then  falls  down  back 
leg. 

3.  The  supply  of  current  to  the  motor  is  interrupted  and  the  elevator 
stops  suddenly;   or  the  voltage  falls,  and  the  motor  fails  to  pull  the  load; 
or  there  is  a  slip  or  failure  in  the  power  transmission. 

4.  Sticks,  tools,  etc.,  get  into  the  boot,  foul  the  belt  and  prevent  it  from 
moving. 

5.  Upper  end  of  discharge  chute  is  set  too  high  for  a  clean  discharge  under 
all  conditions. 

6.  Strings  or  pieces  of  bagging  catch  on  the  upper  end  of  the  chute, 
prevent  a  clean  discharge  and  cause  spill  down  the  back  leg. 

7.  If  the  elevator  is  shut  down  while  loaded  and  is  not  fitted  with  a  back- 
stop, the  elevator  may  run  backward  and  fill  up  the  boot  and  lower  part  of 
the  casing. 

8.  Speed  is  too  high,  grain  hits  the  top  or  front  of  the  hood  and  falls 
down  the  back  leg. 

9.  The  elevator  is  stopped  before  the  supply  of  grain  to  the  boot  is  shut 
off. 

10.  Take-up  tension  is  not  maintained.     (On  this  point,  see  p.  270.) 
When  the  choke  is  such  that  the  belt  slows  down  or  stops  while  the  power 

is  still  on  and  the  head  pulley  continues  to  turn,  the  result  is  that  the  pulley 
rubs  hard  on  the  inside  of  the  belt,  wears  the  plies  away  and  often  generate? 
heat  enough  to  start  a  fire  and  cause  a  dust  explosion.  A  report  on  thf 
cause  of  a  disastrous  explosion  says: 

"  There  was  no  question  after  investigation  but  that  a  choke  had  occurred 
in  an  elevator  leg  at  ten  minutes  to  twelve.  The  men  left  the  plant  shortly 
after,  and  on  their  return  at  noon  smelled  the  odor  of  burning  rubber,  which 
they  thought  was  due  to  a  hot  belt  in  the  basement,  a  belt  which  had  been 
rubbing  to  one  side.  We  found  a  man  who  had  been  to  the  top  floor  of 
the  elevator  and  only  about  two  minutes  before  the  explosion  saw  smoke 
coming  out  of  the  elevator,  and  saw  the  flames  of  the  burning  belt,  and 
only  had  time  to  get  to  the  first  floor  before  the  explosion.  .  .  .  There 
was  no  general  fire;  when  men  entered  the  plant  less  than  half  an  hour 
after  the  explosion,  that  particular  elevator  leg  was  red  from  fire;  it  was  the 
only  one  in  which  there  was  fire.  The  belt  was  burned  in  two."  l 

In  many  chokes  the  belt  slips  but  does  not  stop;  in  this  case  the  pulley 
side  may  be  seriously  torn  and  frayed  by  the  continued  rotation  of  the 
head  pulley,  especially  when  the  lagging  or  covering  of  the  pulley  is  in  bad 
condition,  with  bolts  projecting  (see  p.  250).  The  heating  of  the  belt  due 
to  frequent  slipping  of  this  kind  may,  in  combination  with  excessive  creep 
due  to  high  belt  tension  (see  p.  275),  tend  to  "  age  "  the  friction  in  rubber 
belts  or  cause  canvas  belts  to  dry  out  and  crack.  This  is  more  true  of  oil- 

1  Dr.  H.  H.  Brown,  U.  S.  Dopt.  of  Agriculture,  reporting  to  the  U.  S.  Grain  Corpora- 
tion on  the  cause  of  an  explosion  in  a  grain  elevator  at  Port  Colborne,  Ontario,  in  which 
ten  men  were  killed.  (Proceedings  of  Conference  on  Grain  Dust  Explosions,  April  24, 
1920.) 


FOOT  PULLEYS  TOO  SMALL  .  303 

saturated  belts  (Class  1  impregnation)  than  of  belts  saturated  with  asphaltic 
compounds;  the  latter  resist  heat  better  and  are  not  affected  to  the  same 
degree.  £ 

Foot  Pulleys  Too  Small. — It  is  certain  that  much  of  the  prevalent 
trouble  with  choked  grain  boots  is  due  to  the  use  of  foot  pulleys  that  are 
too  small.  When  a  boot  pulley  revolves  three  or  four  times  as  fast  as  the 
head  pulley  the  forces  which  prevent  the  grain  from  staying  in  the  buckets 
under  the  foot  wheel  are  five  to  seven  times  as  great  as  those  which  throw 
the  grain  out  of  the  buckets  on  the  head  wheel  (see  p.  214).  This  prevents 
the  buckets  from  taking  any  load  until  they  are  on  the  point  of  leaving 
the  foot  wheel  or  are  on  the  straight  lift.  All  the  while  they  are  in  contact 
with  the  foot  pulley  they  merely  stir  up  the  grain,  add  to  the  pull  on  belt 
and  bolts  and  consume  power.  When  the  pulley  is  larger,  the  conditions 
for  pick-up  are  better  (compare  Figs.  202  and  204),  the  boot  is  larger  and 
there  is  more  room  in  it  to  take  care  of  an  accidental  accumulation  of  grain ; 
the  excess  of  feed  over  elevator  capacity,  or  what  spills  down  the  back  leg, 
will  not  pile  so  deep  on  the  rising  side;  the  work  of  digging  will  be  easier 
and  chokes  will  not  be  so  frequent  nor  so  harmful. 

Lack  of  Automatic  Take-up. — For  reasons  stated  on  pages  266  and 
270,  grain-elevator  belts  will  slip  if  the  load  is  heavy  and  if  the  belt  tension 
is  not  sufficient.  As  between  no  load  and  full  load,  a  belt  may  stretch 
some  inches  in  100  feet:  if  c.n  automatic  take-up  is  not  used,  and  if  screws 
are  used  to  tighten  the  belt,  neglect  to  adjust  the  screws  during  the  oper- 

T 

ation  of  the  elevator  may  cause  the  ratio  of  belt  tensions  —  to  fall  to  such 

T  2 

a  point  that  the  head  pulley  will  not  drive  the  belt.  Then  the  belt  slips 
and  a  choke  occurs.  The  same  thing  may  happen  if  the  weight  on  an  auto- 
matic take-up  is  not  sufficient;  but  in  any  case,  an  automatic  take-up  is 
better  than  a  screw  take-up  on  any  grain  elevator;  in  high  elevators  it  is 
really  essential. 

Prevention  of  Chokes  in  Grain  Elevators. — In  the  design  of  the  elevator 
the  bucket  capacity  should  be  larger  than  is  necessary  to  give  the  required 
number  of  bushels  per  hour;  for  reasons  stated  on  page  235  it  should  be 
great  enough  to  cover  the  peak-load  capacity  which,  for  a  minute  or  a  few 
minutes,  may  be  at  a  rate  sufficient  to  exceed  the  hourly  rate  by  a  large 
margin.  An  excess  of  bucket  capacity  is  a  kind  of  insurance;  it  takes  care 
of  emergencies,  and  if  a  choke  does  occur,  the  elevator  can  dig  itself  clear 
in  a  short  time  without  damage  to  the  belt  or  buckets. 

The  lip  of  the  head  chute  should  come  close  to  the  buckets  (Fig.  290) 
and  it  should  be  set  not  less  than  15°  below  the  center  of  the  head  shaft 
if  the  belt  travels  at  the  speeds  of  Table  35;  20°  is  better.  If  the  belt 
speed  is  lower,  Table  36,  the  angle  should  be  30°  for  grain.  Many  high- 
. speed  elevators  have  chutes  set  12°  or  15°  below  the  head  shaft;  but  there  is 
always  the  risk  that  the  speed  may  fall  off,  or  that,  for  some  other  reason, 
the  buckets  may  not  discharge  properly  into  a  chute  set  too  high.  To 
set  the  lip  of  the  chute  at  20°  instead  of  12°  means  an  increase  of  only  7 


304 


ELEVATOR  BOOTS 


or  8  inches  in  the  height  of  an  elevator  with  a  72-inch  head  pulley — not  a 
heavy  price  to  pay  for  some  insurance  against  trouble. 

There  should  be  plenty  of  room  in  the  front  of  the  hood  over  the  head 
pulley,  so  that  the  direct  discharge  and  also  the  splash  from  the  buckets 
will  enter  the  chute  without  striking  the  front  plate  (see  Fig.  290). 

There  are  in  use  a  number  of  safety  devices  to  prevent  grain  from 
dropping  down  the  back  leg  in  case  the  flow  from  the  discharge  spout  is 
stopped  by  the  chute  rilling  up  or  by  a  choke  in  the  spout  itself.  An 
auxiliary  by-pass  spout  is  fitted  to  the  discharge  spout  near  the  head  casing 
so  that  when  the  main  spout  fills  up,  the  grain  will  enter  the  by-pass  and  be 
directed  to  an  emergency  bin,  or  be  dropped  on  a  floor  where  it  can  be  seen, 
or  made  to  enter  a  counterbalanced  tank,  which,  on  receiving  a  certain 
weight  of  grain,  drops,  sounds  an  alarm,  and  closes  the  gate  at  the  boot 
or  else  stops  the  conveyor  which  delivers  to  the  boot. 


FIG.  276. — Reverse-motion  Brake  for  Elevator  Head  Sheave.     (Witherspoon-Englar  Co.). 

On  the  influence  of  automatic  take-ups  and  large  foot  pulleys  in  reduc- 
ing the  risk  of  chokes  in  the  boot,  see  above. 

When  a  choke  does  occur  it  is  important  that  the  rotation  of  the  head 
pulley  should  stop  as  soon  as  the  belt  slows  down;  otherwise  the  belt  may 
be  damaged  or  burnt.  When  the  drive  is  from  a  separate  electric  motor 
the  danger  of  a  burnt  belt  is  reduced  when  the  circuit  breaker  has  an  over- 
load release  set  to  throw  out  before  the  overload  becomes  too  great.  Elec- 
trical safety  devices  are  used  also  to  stop  motors  when  bins  are  full,  to  stop 
the  conveyor  which  delivers  to  the  boot  as  soon  as  current  is  cut  off  from 
the  elevator  motor,  and  to  prevent  the  conveyor  motor  from  starting  until 
the  elevator  is  up  to  full  speed. 

Elevator  Back  Stops. — To  prevent  the  elevator  from  running  backward 
under  load  with  the  power  shut  off  there  may  be  on  the  end  of  the  head  shaft 
a  ratchet  wheel  which  engages  a  pawl  fulcrumed  on  the  beam  that  supports 


ELEVATOR  BACK  STOPS 


305 


one  of  the  shaft  bearings.  To  avoid  noise,  the  pawl  is  usually  fitted  with  a 
friction  device  of  some  kind  which  ikeeps  it  away  from  the  ratchet  teeth  while 
the  shaft  revolves  in  the  operating  direction,  but  allows  it  to  drop  into 
place  and  stop  the  ratchet  wheel  if  the  shaft  should  start  to  turn  backward. 

Fig.  276  shows  a  back  stop  applied  to  a  rope  sheave  on  an  elevator 
head  shaft.  A  hardened  steel  roller  is  contained  in  a  frame  on  which  is 
mounted  a  brake  shoe,  engaging  one  or  two  of  the  grooves  on  the  lower 
or  empty  side  of  the  sheave.  The  roller  bears  against  a  finished  part  on  the 
inside  of  the  sheave  rim  and  is  backed  up  by  a  wedge-shaped  steel  plate. 
In  normal  rotation,  the  roller  stays  at  the  small  end  of  the  wedge  plate,  and 
the  brake  block  hangs  clear, 
but  if  the  sheave  starts  to 
reverse,  the  roller  travels 
toward  the  thick  end  of  the 
wedge  plate  and  brings  the 
brake  block  into  contact  with 
the  grooves  of  the  sheave. 

Fig.  277  shows  the  Gemlo 
back-stop  (patented  1916). 
On  the  inside  of  the  rim  of 
the  brake-wheel  which  is 
keyed  to  the  head  shaft  there 
rests  a  brake  shoe.  The 
shoe  is  jointed  to  a  two- 
armed  lever  which  is  loosely 
mounted  on  the  head  shaft. 
During  normal  rotation  the  shoe  hangs  loose,  but  if  the  shaft  starts  to 
reverse  the  shoe  takes  hold  and  forms  a  toggle-lock  with  the  two-armed 
lever  to  prevent  rotation.  To  unlock  the  brake,  the  long  arm  of  the  two- 
armed  lever  is  moved  so  as  to  break  the  toggle-lock. 


FIG.  277. — Gemlo  Back-stop. 


CHAPTER  XXII 


INCLINED  ELEVATORS 


Inclined  Elevators. — For  the  same  belt  speed  and  same  size  of  foot  wheel 
the  pick-up  at  the  foot  of  an  inclined  centrifugal  discharge  elevator  is  apt 
to  be  better  than  in  a  vertical  elevator,  because  at  the  moment  of  leaving 
the  wheel  to  enter  on  the  straight  inclined  run,  the  bucket  is  tilted  back 
and  the  resultant  of  pressure  due  to  the  combination  of  centrifugal  force 
and  gravity  is  directed  more  toward  the  bottom  of  the  bucket  and  is  not  so 
likely  to  force  material  out  over  the  front  lip.  This  is  not  so  noticeable 
when  the  mass  of  material  in  the  boot  is  small  and  when  the  buckets  do  not 
fill;  but  when  the  mass  is  deeper,  and  the  loading  continues  until  the  lip 
of  the  bucket  is  at  or  above  the  level  of  the  foot  shaft,  then  the  last  material 
delivered  to  the  bucket  is  jerked  toward  the  back  when  the  bucket  enters 
on  the  straight  inclined  run  and  does  not  partly  spill  over  the  front  lip,  as 
happens  when  the  run  is  vertical. 

Fig.  278  illustrates  this  difference  by  showing  that  for  speeds  and  sizes 
of  wheels  as  shown  in  Fig.  206,  the  resultant  pres- 
sure for  the  bucket  on  a  20°  incline  makes  an  angle 
of  32°  with  the  back  of  the  bucket,  while  the 
pressure  for  a  bucket  on  a  vertical  run  is  15  per  cent 
greater  in  amount  and  inclined  at  44°  to  the  back. 

After  passing  the  foot  wheel,  the  belt  and 
buckets  vibrate  to  some  degree,  and  the  material, 
if  free-flowing,  tends  to  shake  down  to  a  surface 


FIG.  278. — Conditions  for 
Filling  Buckets  at  Foot 
Wheel  more  Favorable 
when  Elevator  is  Inclined. 


FIG.  279. — Comparison  of  Loading 
Malleable  Iron  "A"  Buckets  on 
Vertical  Run  or  20°  Incline. 


at  right  angles  to  the  direction  of  gravity — that  is,  the  surface  of  the  material 
in  the  bucket  will  be  approximately  horizontal.  This  means  that  a  bucket 
piled  full  on  leaving  the  foot  wheel  is  apt  to  spill  less  on  an  inclined  run 

306 


PATH  OF  BELT  ON  INCLINED  ELEVATORS 


307 


than  on  a  vertical  run.  Fig.  27ft  shows  that  the  water-level  capacity  of  a 
standard  malleable-iron  Style  A  bucket  is  38  per  cent  more  on  a  20°  incline 
than  on  a  vertical  run.  .While  thi&  is  not  true  to  the  same  extent  of  materials 
which  do  not  flow  freely  and  which  pile  up  at  steep  angles,  still  it  is  generally 
true  that  standard  Style  A  buckets  carry  better  on  inclines  up  to  30° 
from  the  vertical  than  on  the  vertical. 

When  the  bucket  reaches  the  head  wheel  the  material  in  it  comes  under 
the  action  of  centrifugal  force,  and  if  the  speed  is  high  enough,  and  if  the 
material  lies  up  to  the  lip  of  the  bucket,  some  of  it  may  spill  over  the  lip. 
Whether  this  happens  or  not  depends  on  the  shape  of  the  bucket  and  the 
direction  of  the  resultant  pressure  at  the  point  where  the  belt  meets  the 
wheel.  Reference  to  Figs.  202  and  205  will  show  that  the  pressure  at 
position  4  in  ordinary  centrifugal  discharge  elevators  is  less  likely  to  cause 


Ill//   L 
Hi//    'W" 


Head  Pullej 


tenary,  no 
Take-up 
Tension 


FIG.  280.— Hang  of  Return  Belt  on  In- 
clined Elevator  as  Affected  by  Take-up 
Tension. 


FIG.  281. — Forms  of  Catenary  Curves  for 
Return  Belt  for  Different  Angles  of 
Slope. 


spill  than  the  pressure  at  position  3,  because  it  is  less  in  intensity  and  is 
directed  more  toward  the  bottom  of  the  bucket  and  not  so  much  toward  the 
lip.  The  same  thing  is  true  of  any  position  on  the  wheel  between  3  and  4 
where  an  inclined  belt  meets  it;  hence  in  an  inclined  elevator  a  bucket  loaded 
to  the  edge  of  the  lip  is  less  likely  to  spill  on  reaching  the  head  wheel  than  the 
same  bucket  in  a  vertical  elevator  with  the  same  size  head  wheel  and  same 
belt  speed. 

Path  of  Belt  on  Inclined  Elevators. — Fig.  280  represents  an  inclined  belt 
elevator  with  the  up  run  supported  on  idlers  and  the  down  run  hanging 
free.  If  no  tension  is  applied  to  the  belt  at  the  foot  wheel,  the  down  run 
forms  a  catenary.  Fig.  281  shows  the  forms  of  catenary  curves  for  elevators 
inclined  from  45°  to  85°  from  the  horizontal,  and  Table  57  shows  charac- 
teristics of  these  curves.  The  use  of  the  table  can  be  understood  from  an 
example  taken  from  practice.  In  a  heavy  stone  elevator  inclined  65° 


308 


INCLINED  ELEVATORS 


TABLE  57.— FACTORS  FOR  INCLINED  BELT  ELEVATORS  WITH  UP  RUN 
SUPPORTED  AND  RETURN  RUN  HANGING  FREE  (NO  ADDED 
TAKE-UP  TENSION) 


1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

L  = 

K  = 

5- 

D  = 

Factor 

Factor 

Factor 

Factor 

Angle 

Ratio 

Ratio 

Angle 

for 

for 

for 

for 

Angle 

of 

Ti 

Ti 

Sin  A  + 

A 

Length 

Tension 

Locating 

Deflection 

B 

Belt 

Tz 

Tz 

/cos  A 

of 

in 

Maxi- 

of 

Wrap 

for 

for 

=  Factor 

Down 

Down 

mum 

Down 

/=.25 

/=.35 

lorW 

Belt 

Belt 

Sag 

Belt 

45 

.50tf 

l.Q2wH 

.2QH 

.20H 

67°  34' 

157°  26' 

1.99 

2.62. 

.78W 

50 

.39tf 

lAQwH 

.2QH 

.19/f 

71°  36' 

158°  24' 

2.00 

2.64 

.82W 

55 

.30tf 

l.34wH 

.2QH 

.I8H 

75°    9' 

159°  51' 

2.01 

2.66 

.85TF 

60 

.23# 

l.25wH 

.25H 

.16H 

78°  23' 

161°  37' 

2.03 

2.69 

.8QW 

65 

.I7H 

l.lSwH 

.25H 

.14# 

81°    7' 

163°  53' 

2.05 

2.71 

.94TF 

70 

.12H 

l.lZwH 

.24H 

.12H 

83°  32' 

166°  29' 

2.07 

2.77 

.96TF 

75 

.08tf 

l.QSwH 

.23H 

.IOH 

85°  39' 

170°  29' 

2.10 

2.83 

.98TF 

80 

.05# 

l.OSwH 

.22H 

.07H 

87°  28' 

172°  33' 

2.13 

2.87 

.99TF 

85 

.02H 

1.02wH 

.20H 

.04H 

88°  57' 

176°  03' 

2.16 

•2.93 

l.OOW 

90 

.00# 

l.OOwH 

90° 

180° 

2.19 

3.00 

l.OOW 

w  =  weight  of  empty  belt  and  buckets  per  foot  (pounds) . 
W  =  total  weight  of  belt  buckets  and  material  on  loaded  run  (pounds). 
H  =  vertical  height  in  feet. 

from  the  horizontal,  the  belt  was  38-inch  10-ply  and  weighed  12  pounds  per 
foot;  steel  buckets  empty  weighed  50  pounds  per  foot;  the  height  on  the 
incline  was  67  feet  and  the  vertical  height  60  feet. 

From  Column  2,  the  length  of  belt  from  where  it  leaves  the  head  pulley 
to  where  it  meets  the  foot  pulley  is  1.17  X60  =70.2  feet. 

From  Column  3,  the  pull  in  the  return  belt  at  the  top  is  1.18X60X 
(50 +  12)  =4390  pounds. 

From  Column  4,  the  greatest  sag  occurs  at  a  point  in  the  belt  .25  X60  = 
15  feet  vertically  above  the  bottom  of  the  foot  pulley. 

From  Column  5,  the  deflection  at  that  point  from  a  straight  line  touching 
the  two  pulleys  is  .14x60=8.4  feet  (measured  at  90°  to  the  straight  line). 

Column  6  shows  that  the  return  belt  is  inclined  at  81°  from  the  hori- 
zontal (9°  from  vertical)  where  it  leaves  the  head  pulley  and  from  this  we 
find  that  the  angle  of  belt  wrap  on  the  head  pulley  is  about  164°  (see  Col- 
umn 7). 

When  by  means  of  take-ups  or  adjustable  bearings,  tension  is  applied 
to  the  belt,  the  curve  changes  its  shape,  becoming  more  like  a  parabola; 
the  deflection  D  becomes  less  and  the  point  of  maximum  sag  rises  slightly. 
In  practice  it  is  generally  necessary  to  put  tension  in  the  return  belt  to 
stop  it  from  swaying  too  much  and  also  to  increase  the  driving  effect  at  the 
head  pulley  by  making  T^  larger  (see  p.  309).  Nevertheless,  the  catenary 
should  always  be  laid  out  to  find  the  length  of  the  belt,  to  locate  the  lip 
of  the  head  chute  and  to  show  what  clearance  is  required  back  of  the  elevator 
in  case  the  belt  should  run  slack. 


CALCULATION  OF  APPLIED  TENSION 


309 


On  the  assumption  that  the,  curve  is  a  parabola,  the  deflection  of  the 
belt  from  the  straight  line  can  be^  obtained  thus:    In  Fig.  282  divide  the 
straight  line  into  4  eqtfal  parts.     Calculate 
the  pull  in  the  return  belt  at  the   top  pulley 
from  Column  3,  Table  57,  add  to  it  the  tension 
applied  to  the  return  belt   by  the  take-ups 
and  call  the  sum  T2.      Then  if  s  =  horizontal 
distance  over  which  the  belt  hangs  in  feet 
and  w  =  weight  per  foot  of  return  belt  and 
buckets,  then  the  vertical  deflection  CD,  in 


feet,    at    the   middle    point    is    h  = 


Ws* 


(see 


Kent's  M.  E.  Pocket-Book).  The  vertical 
deflection  at  the  quartering  points  G  and  F 
is  \h. 

To  draw  the  curve,  locate  E  at  a  distance 
h  below  D;    then  BE  will  be  tangent  to  the 
upper  part  of  the  curve  where  the  belt  leaves  FIG.  282.— Lay-out  of  Return  Belt 
the  pulley  and  A  E  will   be  tangent  to  the  as  a  Parabola, 

lower  part  where  it  goes  on  to  the  foot  pulley. 

Calculation  of  Applied  Tension. — If  in  Fig.  280  W  represents  the  total 
weight  of  the  loaded  up  run,  belt,  buckets  and  material  carried,  then  the 
downward  component  of  W  which  puts  a  direct  pull  in  the  belt  is  W  sine  A, 
and  the  component  which  makes  the  idlers  turn  is  W  cosine  A  (see  also 
Fig.  99);  if /is  a  coefficient  which  includes  the  friction  of  the  belt  idlers  and 
the  slight  lifting  of  the  load  in  passing  over  the  idlers,  then  fW  cosine  A  is 
the  belt  pull  due  to  contact  with  the  idlers.  The  total  belt  pull  due  to  the 
weight  is,  therefore, 

Pull  =  TF(sine  A  +/  cosine  A). 

To  this  should  be  added  the  pull  due  to  pick-up  (see  p.  273). 

Column  10,  Table  57,  gives  values  of  (sine  A  +/  cosine  A)  in  which 
/  varies  from  .05  on  steep  elevators  to  .10  for  an  incline  of  45°,  the  higher 
coefficients  allowing  for  the  greater  motion  of  the  belt  and  load  in  passing 
over  idlers  where  the  incline  is  not  steep.  The  figures  in  Column  10  assume 
that  the  material  is  fed  to  the  buckets  from  a  chute  and  is  not  dug  from  a 
boot. 

In  large  belt  elevators  handling  stone  and  ore  in  continuous  buckets  the 
weight  of  material  carried  is  great  in  proportion  to  the  weight  of  the  empty 
belt  and  buckets;  and  for  reasons  already  mentioned  in  Chapter  XX  it  is 
necessary  to  tighten  the  belt  by  means  of  the  take-ups.  In  the  stone 
elevator  referred  to  above  the  buckets  held  at  full  capacity  130  pounds  of 
stone  per  linear  foot.  The  length  of  the  inclined  loaded  run  is  67  feet; 
its  weight  is  therefore  67(12+50  +  130)  =12,864  pounds  and  from  Column 
10,  Table  57,  the  pull  at  the  head  due  to  the  weight  is  .94  X  1,2864  =  12,093 
pounds,  For  the  pick-up  of  material  we  may  allow  the  equivalent  of 


310  INCLINED  ELEVATORS 

11  feet  on  the  lift  (see  p.  273)  or  1430  pounds,  making  a  total  pull  T\  = 
13,523  pounds. 

Since  the  pull  at  the  top  of  the  return  belt  is  4390  pounds,  the  ratio  of 

T 

—  for   a    natural    sag    of    the    return    belt  without    applied    tension    is 

Tz 

•I  q    KOO  '7T 

— ! =3.08.     This  is  greater  than  2.71,  which  is  the  working  ratio  of  — 

4390  T, 

when/ =  .35  (see  Column  9),  hence  not  even  a  lagged  pulley  will  drive 
the  elevator  unless  some  take-up  tension  is  added.  To  find  out  what 
tension  x  is  necessary,  assume  that  the  head  pulley  is  lagged  and  that  the 

T 
ratio  of  —  is  to  be  2.7,  then 

Tz 

13,523  +z  =  2.7(4390+*) 

from  which  x  =  980  pounds. 

When  the  take-up  puts  980  pounds  tension  into  each  run  of  the  elevator 
the  pull  in  the  up  belt  is  13,523+980=14,503  pounds  and  the  36-ounce 

14  503 

duck  is  stressed  to  —       —  =38  pounds  per  inch  per  ply. 
38  X 10 

Discharge  from  Inclined  Elevators  with  Spaced  Buckets. — In  a  vertical 
elevator  some  clearance  space  must  be  left  between  the  upper  edge  of  the 
discharge  chute  at  the  head  and  the  lips  of  the  descending  buckets.  Although 
the  space  may  be  small,  some  drip  from  the  buckets,  or  material  delayed  in 
discharge,  may  fall  through  it  and  be  wasted;  but  if  the  elevator  is  inclined, 
the  chute  may  be  placed  partly  under  the  path  of  bucket  travel  so  that  some 
or  all  of  the  spill  may  be  caught. 

This  point  is  not  of  much  importance  in  handling  free-flowing  materials 
like  grain.  These  can  be  picked  up  and  discharged  at  high  speed  (see 
Table  35);  but  if  the  material  is  damp  and  sluggish,  or  if  it  is  hard,  lumpy 
and  abrasive,  lower  speeds  like  those  of  Table  36  are  preferable;  or  it 
may  be  advisable  to  pick  up  and  discharge  difficult  material  at  speeds  still 
lower  than  Table  36.  If  the  elevator  is  run  at  speeds  lower  than  Table  36 
it  must  be  inclined  in  order  to  catch  the  spill  and  the  delayed  discharge. 
This  condition  of  discharge  is  illustrated  in  Fig.  214  and  it  is  shown  also 
in  Fig.  283.  If  Fig.  283  is  turned  so  that  the  line  A — B  is  vertical,  the  view 
represents  an  elevator  inclined  at  40°  from  the  vertical  and  run  at  a  speed 
less  than  Table  36.  A  chute  at  C  will  catch  the  material  which  begins 
to  fall  from  the  buckets  high  on  the  wheel,  and  also  some  of  what  is  scattered 
by  interference  between  bucket  D  and  the  discharge  from  bucket  E. 

Size  of  Head  Wheels. — The  bad  discharge  caused  by  the  interference 
mentioned  above  causes  a  waste  of  material  and  power,  because  even  in  an 
inclined  elevator  a  chute  set  partly  under  the  head  will  not  catch  all  of  the 
scattered  material.  It  is  evident  from  Fig.  283  that  if  the  head  wheel 
were  18  inches  in  diameter  instead  of  36  inches  the  buckets  which  come 
every  12  inches  would  be  76°  apart  on  the  wheel  instead  of  38°  apart  as 


DISCHARGE  WITH  SMALL  HEAD  WHEEL 


311 


shown  in  the  figure.     With  this  greater  angle  between  the  adjacent  buckets, 
the  discharge  would  be  cleanei1  and  interference  would  not  occur. 

This  is  shown  better  in  Fig.  ^84,  representing  the  head  of  an  elevator 
inclined  30°  from  the  vertical.  With  the  large  wheel,  the  positions  of 
consecutive  buckets  are  1,  2,  3,  etc.  With  the  same  linear  spacing  of 
buckets  on  a  head  wheel  of  half  the  size  the  corresponding  positions  are 
1,  4,  5,  etc.  If  the  speed  is  such  that  discharge  begins  at  1,  and  follows  the 


FIG.  283. — Condition  of  Discharge  for  which  it  is  Necessary  to  Incline  the  Elevator. 

parabola  1 — (r,  some  of  it  will  hit  the  bucket  at  2;    but  such  a  discharge 
would  clear  the  bucket  at  4  just  leaving  the  small  head  wheel. 

Discharge  with  Small  Head  Wheel. — As  a  matter  of  fact,  the  discharge 
from  a  bucket  at  1  on  the  small  wheel  does  not  follow  the  path  1 — G,  but 
goes  out  on  the  parabola  1 — P,  because  for  a  given  belt  speed,  centrifugal 
force  at  a  head  wheel  varies  inversely  as  R — that  is,  jt  is  twice  as  great  on 
a  wheel  of  half  the  size,  for  a  given  belt  speed.  The  two  arrows  drawn  from  1 
represent  by  their  position  and  their  length,  as  drawn,  the  direction  and 
intensity  of  the  resultant  forces  which  cause  material  to  leave  the  bucket 
at  1,  and  the  parabolas  are  tangent  to  them. 


312 


INCLINED  ELEVATORS 


This  explains  why,  in  an  inclined  elevator,  run  at  a  given  speed  in  feet 
per  minute,  a  small  head  wheel  makes  a  better  discharge: 

1.  The  buckets  turn  more  quickly  under  the  wheel  and  get  out  of  the 
way  of  discharged  material. 

2.  Centrifugal  force  is  more  active  and  there  is  more  "  throw  "  to  the 
discharge. 

Point  at  which  Discharge  Begins. — In  considering  the  action  at  the 
head  of  an  inclined  elevator  run  at  comparatively  slow  speed,  the  point  at 
which  discharge  begins  may  be  referred  to.  According  to  theory,  the 
material  begins  to  leave  the  bucket  on  the  descending  side  of  the  wheel  at 
the  point  at  which  centrifugal  force  equals  the  radial  component  of  the 
weight.  In  Fig.  285  the  forces  which  determine  discharge  are  (1)  gravity, 
acting  downward  with  a  force  W,  or  if  measured  on  the  radial  line, 


FIG.  284.— Effect  of  Wheel  Diameter  on  Dis- 
charge at  Head  of  Inclined  Elevator. 


FIG.  285.— Point  at  Which 
Discharge  Begins. 


W  cosine  A,  where  A  is  the  angle  from  the  vertical;    (2)  centrifugal  force, 

Wv2 
acting  radially  outward  with  a  value  - —  (see  p.  212).     The  mass  within 

gR 

the  bucket  will  be  in  equilibrium,  tending  neither  to  fall  out  nor  fly  out 

Wv2  v2 

when =W  cosine  A  or  when  cosine  A  = — . 

gR  gR 

When  v2  =gR,  as  at  the  high  speeds  of  Table  35  (see  p.  212),  cosine  A  =  1, 
A  =  0°,  and  discharge  is  ready  to  begin  at  the  top  of  the  wheel;  when 
v2=%gR,  as  at  the  lower  speeds  of  Table  36  (see  p.  216),  cosine  -4=1, 
A  =48°,  and  discharge  may  be  said  to  begin  about  halfway  down  in  the 
quadrant  of  discharge.  It  is  a  fact,  however,  that  some  material  always 
leaves  the  bucket  sooner  than  would  be  indicated  by  the  angle  A  calculated 
in  this  way.  It  is  caused  by  the  shifting  of  the  load  within  the  bucket; 
at  position  4,  Fig.  205,  the  resultant  pressure  is  directed  toward  the  bottom 
of  the  bucket;  at  6  it  is  directed  toward  the  back;  since  the  surface  of  the 
material  tends  to  arrange  itself  at  right  angles  to  the  line  of  pressure,  the 


SIZE  OF  HEAD  WHEELS  313 

load  shifts  in  the  bucket;  at  6  it  flattens  out  on  the  back  of  the  bucket, 
and  if  the  bucket  is  full  or  nearly  full  some  of  the  material  may  spill  out 
over  the  leading  edge  of  the  bacK.  This  can  be  counteracted  by  making 
buckets  with  high  backs  or  hooded  backs,  but  ordinary  buckets  on  belt 
run  at  slow  speed  are  always  apt  to  spill  if  they  carry  a  full  load. 

Spill  due  to  Shift  of  Load  within  the  Bucket. — This  spill  is  not  so  likely 
to  occur  in  high-speed  elevators,  because  discharge  occurs  before  the  load 
has  time  to  shift  in  the  bucket,  and  if  it  does  occur,  it  may  be  affected  by 
centrifugal  force  to  a  degree  sufficient  to  describe  a  parabola  that  will  land 
it  in  the  head  chute;  but  in  elevators  run  at  speeds  less  than  Table  36, 
any  material  spilled  between  the  top  of  the  wheel  and  the  point  of  theoretical 
discharge  will  fall  so  nearly  vertical  that  the  only  way  to  catch  it  is  to  incline 
the  elevator  and  set  the  chute  well  under  the  head  wheel.  The  loss  of  some 
of  this  material  is  unavoidable,  being  due  to  interference  with  the  descend- 
ing buckets,  but  some  material  will  enter  the  chute. 

Size  of  Head  Wheels  and  Spacing  of  Buckets. — When,  for  the  sake  of 
slow  speed  in  pick-up  or  discharge,  inclined  elevators  are  run  at  speeds  one- 
half  of  those  in  Table  35,  the  effect  of  centrifugal  force  becomes  very 
small  and  the  main  discharge  from  a  bucket  occurs  more  than  halfway 
down  in  the  discharge  quadrant — that  is,  angle  A,  Fig.  285,  is  over  70° 
from  the  vertical.  The  path  of  discharge  is  then  nearly  vertical,  and  in 
order  to  avoid  interference  the  leading  bucket  should  be  so  far  ahead  on  the 
arc  of  travel  that  the  discharged  material  cannot  fall  on  it.  The  spacing 
of  buckets  in  slow-speed  inclined  elevators  can  therefore  best  be  expressed 
as  an  angular  distance  on  the  circumference  of  the  head  wheel;  and  the 
diameter  of  the  head  wheel  should  be  such  that  a  normal  bucket  spacing 
should  not  cover  too  small  an  arc.  In  other  words,  the  head  wheel  must 
not  be  too  large. 

When  elevators  inclined  at  about  30°  from  the  vertical  are  run  at  speeds 
one-half  those  of  Table  35  or  less  buckets  of  standard  size  and  shape  make  a 
satisfactory  discharge  if  they  are  spaced  90°  apart  on  the  head  wheel — that 
is,  if  the  circumference  of  the  head  wheel  is  four  times  the  bucket  spacing. 

Table  58  shows  wheel  sizes  and  revolutions  and  bucket  spacings  for 
belt  speeds  one-half  those  of  Table  35.  It  gives  also  the  projections 
of  buckets  proper  for  the  given  spacings.  In  elevators  designed  in  this  way 
centrifugal  force  equals  one-fourth  the  force  of  gravity  and  the  angle  A, 
Fig.  293,  at  which  the  main  discharge  occurs  is  75|°  (cosine  =£). 

At  speeds  lower  than  those  of  Table  58  the  influence  of  centrifugal 
force  is  practically  zero,  but  the  data  given  still  hold  good  as  to  wheel  sizes, 
bucket  spacings  and  bucket  projections. 

Advantages  of  Inclined  Elevators. — Inclined  elevators  are  often  preferred 
to  vertical  elevators  for  reasons  other  than  those  of  pick-up  and  discharge 
at  slower  speed.  If  there  is  a  horizontal  traverse  from  the  loading  point 
to  the  discharge  point  of  not  more  than  one-half  the  height  through  which 
the  material  is  to  be  lifted,  setting  the  elevator  on  an  incline  will  both  elevate 
and  convey  the  material  without  the  use  of  a  feed  conveyor  at  the  foot  or  a 


314 


INCLINED  ELEVATORS 


TABLE    58.  — HEAD     WHEELS,    'SPEED,    BUCKET     SPACING,    INCLINED 
ELEVATOR,  CENTRIFUGAL  DISCHARGE  AT  LOW  SPEED 


Diam- 
eter of 
Wheel, 
Inches 

Revo- 
lutions 
per 
Minute 

Belt 
Speed, 
Feet  per 
Minute 

Bucket 
Pro- 
jection, 
Inches 

Bucket 
Spacing, 
Inches 

Diam- 
eter of 
Wheel, 
Inches 

Revo- 
lutions 
per 

Minute 

Belt 
Speed, 
Feet  per 
Minute 

Bucket 
Pro- 
jection, 
Inches 

Bucket 
Spacing, 
Inches 

12 

35 

110 

3 

9.4 

27 

24 

175 

7 

21.2 

15 

31 

124 

3^ 

11.8 

30 

23 

180 

8 

23.5 

18 

28 

132 

4 

14.1 

33 

22 

190 

9 

25.9 

21 

27 

147 

5 

16.5 

36 

21 

198 

10 

28.2 

24 

25 

157 

6 

18.8 

bearing-off  conveyor  at  the  head.  When,  however,  the  angle  of  incline  is 
more  than  25°  from  the  vertical,  it  becomes  necessary  to  support  the  loaded 
run  and  to  provide  space  for  the  sag  of  the  return  run  (see  Table  57). 

One  of  the  merits  of  the  inclined  elevator  shown  in  Fig.  257  is  that 
the  fine  damp  sand  which  discharges  late,  or  which  shakes  off  the  buckets  at 
the  head,  does  not  fall  down  on  the  foot  pulley  as  it  would  if  the  elevator 
were  vertical.  The  vertical  back  wall  of  the  casing  permits  the  spill  to  fall 
straight  down  into  a  clearance  space  in  back  of  the  belt,  from  which  it  is 
picked  up  by  the  buckets  when  the  accumulation  becomes  large  enough. 
Keeping  the  sand  from  falling  onto  the  pulley  lessens  the  injury  to  the 
pulley  side  of  the  belt  due  to  sand  and  grit  between  it  and  the  pulley  (see 
p.  290). 

When  a  vertical  elevator  with  centrifugal  discharge  is  shut  down  in  an 
emergency  while  loaded,  the  speed  falls  off,  the  buckets  make  a  bad  dis- 
charge and  the  material  misses  the  chute  and  falls  down  into  the  boot,  with 
the  possibility  that  the  boot  may  be  choked  when  the  elevator  starts  again. 
In  an  inclined  elevator  with  the  chute  partly  under  the  head  wheel  most  of 
the  spill  in  such  a  case  will  be  caught  and  will  not  choke  the  boot. 

In  handling  mineral  pulps  and  slimes  an  elevator  slightly  off  the  vertical 
is  preferable  for  the  reasons  stated  on  page  306:  the  spill  in  passing  from 
the  foot  wheel  to  the  straight  run  is  less;  the  buckets  hold  more  on  the 
incline;  the  spill  is  less  on  meeting  the  head  wheel;  and  if  the  incline  is 
enough  to  permit  the  head  chute  or  receiver  to  be  placed  partly  under  the 
path  of  the  descending  buckets  some  of  the  solids  which  are  discharged 
late  will  be  caught  instead  of  spilling  down  into  the  casing.  The  inclina- 
tion is  generally  limited  to  10°  or  15°  from  the  vertical;  otherwise,  the 
up  run  must  be  carried  on  idlers,  and  they  are  troublesome  in  a  wet 
elevator. 

A  general  advantage  of  a  belt  elevator  inclined  at  20°  or  more  from  the 
vertical  is  that  the  sag  between  head  and  foot  keeps  the  belt  in  contact 
with  the  foot  pulley  in  spite  of  occasional  neglect  of  the  take-ups.  If  the 
foot  pulley  in  a  vertical  elevator  is  not  set  down  to  follow  the  stretch  of  the 
belt  the  contact  between  them  may  be  so  slight  that  the  pulley  and  shaft 
will  not  turn,  and  then  the  belt  will  rub  and  wear.  If  the  slack  is  so  great 


DISADVANTAGES  OF  INCLINED  ELEVATORS  315 

that  the  belt  is  loose  on  the  pulley  the  buckets  are  not  backed  up  by  the 
pulley;  they  do  not  fill  well,  and  the  capacity  of  the  elevator  falls  off. 

The  length  of  the  return  belt  is^also  greater  than  in  a  vertical  elevator 
of  the  same  height;  and  when  the  take-ups  are  set  down  to  apply  added 
driving  tension  to  the  belt,  the  belt  can  work  longer  and  stretch  more 
before  the  effect  of  the  take-up  tension  is  lost. 

This  may  be  expressed  in  a  different  way  by  saying  that  if  the  inner 
curve  in  Fig.  280  represents  the  hang  of  the  belt  when  pulled  to  its  maximum 
operating  tension,  and  if  the  catenary  shows  the  hang  of  the  belt  under  no 
take-up  tension,  then  the  difference  in  length  between  the  two  is  the  amount 
the  belt  may  stretch  in  service  before  it  loses  all  the  effect  of  the  take-up 
tension.  This  difference  may  be  a  foot  or  more  in  an  inclined  elevator,  but 
the  corresponding  difference  in  a  vertical  elevator  may  be  only  a  few  inches. 
When  the  vertical  belt  stretches  a  few  inches  in  service  it  may  slip  on  the 
head  pulley  and  act  badly  at  the  foot  unless  the  take-ups  are  set  down; 
but  an  inclined  belt  may  stretch  several  times  as  much  before  it  is  necessary 
to  adjust  the  take-ups  again. 

For  the  reasons  just  stated,  inclined  belts  do  not  have  to  be  shortened 
and  respliced  so  frequently  as  vertical  belts,  and  a  new  inclined  belt  will 
run  longer  before  it  has  to  be  cut  and  shortened. 

In  stone  and  rock  elevators  inclined  at  20°  or  25°  from  the  vertical 
the  sag  of  belt  acts  to  some  extent  as  a  relief  if  a  lump  catches  between  the 
belt  and  the  foot  pulley.  In  a  vertical  elevator  a  tight  belt  is  not  likely 
to  stretch  still  further  and  prevent  injury  when  an  accident  of  this  kind 
occurs.  In  an  inclined  elevator,  however,  with  some  free  sag  at  the  bottom 
of  the  down  belt,  there  may  be  "  give  "  enough  to  prevent  the  stone  from 
punching  a  hole  in  the  belt.  This  is  merely  an  incidental  reason  for  inclining 
a  stone  elevator  with  continuous  buckets  on  a  belt;  the  main  reason  is  that 
the  incline  permits  the  buckets  to  be  loaded  from  a  chute  without  spill 
(see  p.  241). 

Disadvantages  of  Inclined  Elevators. — When  an  inclined  elevator  is 
high,  or  is  set  at  a  considerable  angle  from  the  vertical,  it  is  necessary  to 
support  the  loaded  run  to  keep  it  from  flapping  and  spilling  material  from 
the  buckets.  The  idlers  used  for  this  purpose  are  flat-face  pulleys  like  those 
made  for  the  return  run  of  belt  conveyors;  sometimes  in  heavy  elevators 
with  continuous  buckets  they  are  pipe  rolls  set  every  6,  8  or  10  feet.  Bear- 
ings for  idlers  on  an  inclined  elevator  are  often  so  located  that  it  is  hard  to 
inspect  and  oil  them,  and  they  are  likely  to  suffer  from  neglect.  Light 
elevators  with  spaced  buckets  can  be  put  up  without  idlers  if  the  slope  is 
not  far  off  the  vertical,  but  heavy  belts  with  continuous  buckets  generally 
require  them. 

A  drawback  to  the  use  of  inclined  elevators  is  the  greater  amount  of 
floor  space  required  and  the  larger  and  more  expensive  casing  necessary 
to  enclose  them. 


CHAPTER  XXIII 


ELEVATOR  CASINGS 

AN  elevator  casing  serves  several  purposes:  (1)  to  confine  dust  and 

catch  material  which  spills  at  the  head,  and 
direct  it  to  the  boot  where  it  can  be  picked 
up  again;  (2)  to  act  as  a  guard  around  the 
moving  belt  and  buckets;  (3)  occasionally, 
to  act  as  a  support  for  the  head  machinery. 

Wood  casings  are  generally  cheaper 
than  steel  casings,  but  in  many  places  they 
are  barred  on  account  of  the  risk  of  fire. 
They  are,  however,  preferred  for  wet  ele- 
vators for  mineral  pulps  and  ores.  The  grit 
carried  by  the  water  that  continually 
splashes  and  drips  from  the  buckets  causes 
destructive  wear  in  thin  metal  casings,  but 
plank  resists  it  better,  and  when  repairs  are 
necessary,  they  can  be  made  quickly  and 
cheaply.  :For  a  form  of  such  a  wooden 
casing,  see  Fig.  257. 

Steel  casings  are  made  in  several  styles. 
The  single  leg  (Fig.  286)  is  generally  used 
for  chain  elevators,  but  not  often  in  belt 
elevators  except  in  small  sizes.  For  belt 
elevators,  the  double  leg  (Fig.  287)  is  more 
common;  the  back  sheet  of  each  leg  is  quite 
close  to  the  back  of  the  belt;  it  guides  it 
and  prevents  it  from  flapping  or  swaying. 
Casings  with  round  legs  (Fig.  288)  have 
been  used  in  Europe  and  to  some  extent  in 
this  country.  When  the  projection  of  the 
bucket  is  at  least  half  the  width  of  the  belt 
the  circumference  of  an  enclosing  circle  is 
noticeably  less  than  the  periphery  of  an 
enclosing  rectangle  and  the  weight  of  the 
round  leg  is  less;  but  when  the  buckets  are 
relatively  short  in  projection  as  compared 
with  the  width  of  the  belt  there  is  not  much 
FIG.  286.— Single  Leg  Steel  Casing,  difference  between  the  two  shapes  as  to  weight. 

316 


ELEVATOR  CASINGS  317 

The  round  leg  requires  only  two  lines  of  punching  and  one  line  of  riveting 
while  a  rectangular  leg  requires1  at  least  twice  as  much;  but  the  latter  has 
the  advantage  of  allowing  easy  access  to  the  belt  and  buckets  by  the  removal 
of  a  sheet,  and  the  sections  of  the  rectangular  casing  are  easily  and  cheaply 
joined  by  straight  angles  instead  of  forged  angle  rings  or  cast-iron  flanges. 


FIG.  287.— Double  Leg  Steel  Casing.  FIG.  288.— Steel  Casing  with  Pipe  Legs. 

The  simplest  rectangular  casing  for  a  double-leg  elevator  is  shown  at 
4  in  Fig.  289.  It  is  cheap,  but  unless  the  plates  are  carefully  squared  and 
accurately  bent  in  the  shop  the  assembled  sections  will  come  crooked  or  with 
a  longitudinal  twist  which  is  troublesome  in  erection.  Casings  for  wide 
buckets  are  generally  made  of  four  pieces  with  the  narrow  end-plates  riveted 


318 


ELEVATOR  CASINGS 


to  angles,  or  crimped  or  flanged  as  shown  at  1,  2,  3.  Casings  with  angle 
corners  are  easier  to  make  dust-tight  than  those  with  flanged  corners,  and 
they  are  more  likely  to  be  straight  and  free  from  twist. 

Dust-tight  Casings. — Casings  of  light  sheet  steel,  No.  14  gauge  and  less, 
cannot  be  made  perfectly  dust-tight  by  riveting  or  bolting,  because  the 


1 

1      Bucket  Widthl 

'    t 

;    I   j 

lr_  TT 

I  ^JSS  ' 

B 

\ 

^  ^3 

!               i 

4 

'  / 

Li=  —  w  —  =^ 

i              f 

Bucket 

Side  Plates  Riveted  to  1  ^"Angles               Side  PlaUs  Crimped                              Side  Plates  Flan-ed 
Front  and  Iij^k  Plates  Bolted  on         Front  and  Back.  Plates  Bolted  on        Front  and  Back  Plates.  Bolted  cm 
All  Bolts  and  Ki\ets  &  4  Pitch                       %'  Bolts  12  Pitch                                 Jj'Uolts  3"Pitch 

i                        ~1 

FIG.  289. — Cross-sections  of  Steel  Elevator  Legs. 

edges  of  the  sheets  are  stretched  slightly  in  punching  and  pucker  slightly 
between  the  rivet  or  bolt  holes.  When  light  casings  must  be  made  so 
tight  that  dust  will  not  leak  out  at  the  seams  nor  at  the  small  crevices 
and  the  corners  of  plates  and  angles,  then  the  joints  must  be  made  with 
gasket  strips,  or  the  surfaces  in  contact  may  be  coated  with  thick  paint 
before  the  parts  are  riveted  or  bolted  together. 


DETAIL 


tare:"^  ;;TT 


FIG.  290. — Head  of  Shipping  Elevator,  Public  Grain  Elevator,  New  Orleans.     (Ford, 
Bacon  &  Davis,  Engineers). 

Doors  in  Casings. — In  single-leg  casings  it  is  often  not  convenient  nor, 
considering  the  stability  of  the  casing,  is  it  safe  to  remove  an  entire  side 
plate  to  give  access  to  both  sides  of  a  run  of  belt  as  is  necessary  for  inspection 
and  for  removing  or  attaching  buckets.  Such  casings  should  be  provided 
with  doors  on  each  side  at  the  levels  of  various  floors  or  where  it  is  con- 
venient to  reach  the  interior  of  the  casing.  If  the  doors  are  bolted  the 
bolts  should  be  entirely  on  the  outside  of  the  casing,  so  that  they  will  not 
be  lost  inside  when  the  nuts  are  removed. 


CASINGS  FOR  ELEVATOR  HEADS 


319 


Casings  for  Elevator  Heads. — In  the  design  of  the  head  of  the  casing 
it  is  important  to  place  the  lip  o^  the  discharge  chute  low  enough  to  catch 


FIG.  291. — Man  Elevator  used  in  Flour  Mills  and  Grain  Elevators. 

the  discharge  from  the  buckets  at  all  times.     On  the  conditions  which  are 
at  times  unfavorable  to  a  clean  discharge,  see  pages  302,  303. 

Fig.  290  shows  the  head  of  a  large  grain  elevator  of  recent  design  with 


320  ELEVATOR  CASINGS 

the  lip  placed  lower  than  has  been  customary.  The  angle  from  the  center 
of  the  head  shaft  down  to  the  upper  edge  of  the  rubber  belt  which  forms  the 
lip  (see  detail)  is  25°.  All  the  joints  at  and  above  the  level  of  the  head 
shaft  are  bolted,  as  is  the  sloping  plate  which  joins  the  two  legs  below  the 
head  pulley.  The  figure  shows  the  bar  screen  referred  to  on  page  261  and 
the  door  which  gives  access  to  it. 

Other  Forms  of  Belt  Elevators. — Cleats  or  projections  are  sometimes 
fastened  to  belts  to  convey  small  boxes,  packaged  goods,  bricks,  etc.,  in 
inclined  conveyors  where  the  angle  of  slope  is  more  than  20°  or  30°. 

Some  large  vertical  elevators  for  boxes  and  barrels  have  been  built 
with  rigid  or  tipping  arms  attached  to  rubber  or  canvas  belts,  but  they 
suffer  from  the  drawback  that  the  arms  for  heavy  work  cannot  be  bolted 
to  a  belt  so  securely,  nor  is  the  guiding  of  the  loaded  run  so  easily  arranged 
as  when  the  arms. are  fastened  to  chains. 

Belt  elevators  with  shelves  (Fig.  291)  are  used  to  carry  men  up  and 
down  from  floor  to  floor  in  grain  elevators,  flour  mills,  etc.  The  belt  is 
usually  12  inches  wide,  4  or  5  ply  thick  and  runs  over  20-inch  head  and 
foot  pulleys  at  a  speed  of  60  to  80  feet  per  minute. 


INDEX 


"A"  buckets,  225,  230,  231 
"AA"  buckets,  225,  230,  231,  232 
Abrasion  of  belts,  11,  12,  18,  19,  26,  133, 

142,  152,  154 

Absorption  of  moisture  by  belt,  55,  56,  184 
Accessibility  for  cleaning,  177,  181,  182,  183 
lubrication,  83,  84,  87,  88,  94,  181, 

182,  183 

Accessories  for  belt  conveyor,  1,  205 
Accidents  to  buckets,  262,  288 
conveyor  belts,    135,    136,   137,    156, 

159,  165,  166,   167,   180,  182,   187, 

196,  197,  199,  200 
elevator  belts,  227,  236,  243,  250,  261, 

262,  275,  281,  288,  290 
Acid  injures  belt,  199 
Acklin  idler,  88 
"  Acme  "  bucket,  225,  229 
Adherence  of  dirt  to  belt,  120,  122,  123,  128, 
176,  182,  183 

pulleys,  122,  180 

Advantages  of  ball-bearing  idlers,  90,  92, 

94,  108,  107,  108 

belt  conveyor,  1,  151,  202 

other  conveyors,  203,  205 

roller-bearing  idlers,  92,  94,  95,  106, 

107,  108 

Aging,  22,  23,  29,  32,  36,  38,  44,  197,  205 
Air  resistance,  271,  274 
Alignment,  bad,  effect  of,  197 
"Alligator  "  belt  fastener,  58 
Anderson  double  belt,  192 
Angle  of  bucket,  225 

incline  for  various  materials,  142 

,  too  steep,  118,  142,  143,  154 

—  loading  chute,  134,  154 
—  pulley  contact,  209,  308 

troughing,  13,  15,  16,  18,  79,  86,  145 

wrap,  109,  110,  209,  308 

Apron  feeder,  compared  with  belt,  204 

Arm  elevator,  320 

Artificial  tension  for  belts,    299,  309;    see 

Take-up  tension 
Ashes,  belt  conveyor  for,  204 
— ,  elevator  for,  282 
Asphalt  compounds  for  canvas  belt,  48,  55, 

275 
Assembly  of  belt,  balata,  2,  50 

,  rubber,  2,  20,  21,  24,  25,  35,  41 

,  solid-woven,  2,  51 

,  stitched  canvas,  2,  47 


Attendance,  expense  of,  87,  92,  94,  107,  159, 

165,  183 
Auld,  E.  C.,  72 

Auxiliaries  for  belt  conveyors,  205 
Auxiliary  drives,  124,  126 


B 

"  B  "  bucket,  225,  230,  231,  233,  235 

,  pick-up  of,  235 

Back-feed  into  boot,  217,  222,  288 

Back-stop  for  elevator,  301,  303,  304 

Bags,  conveyor  for,  184 

Balata,  2,  49 

—  belt,  see  Belts  for  Conveyors,  Belts  for 
Elevators 

Baldwin,  C.  K.,  98,  164,  168 

Ball-bearing  idlers,   88,   89,   92,    106,   107; 
see  Idlers 

Baltimore  &  Ohio  R.R.,  172,  173 

Barber-Greene  Co.,  188 

Barrel  elevator,  320 

Earth,  Carl,  267,  276 

Bartlett  and  Overstrom,  174 

Bearings  for  boots,  293,  297,  298 

package  conveyor,  185,  186 

— ,  oilless,  185,  293 

Beaumont  Co.,  R.  H.,  181,  182 

Bee  idler,  88 

Belt  conveyor,  Chapter  I  and  specific  refer- 
ences below. 

,  accessories,  3,  205 

,  advantages  of,  1,  151,  202 

,  auxiliaries  for,  205 

,  bridges  for,  182,  183 

,  capacity  of,  139,  143,  144,  145,  148, 

„       150 

,  compared  with  other  machines,  204, 

205 

,  design  of,  115,  116,  117,  118,  142,  202 

,  disadvantages  of,  205 

,  discharging,  5,  Chapter  VIII 

,  driving,  3,  Chapter  V 

,  Evans'  (Oliver),  6 

,  for  boiler-houses,  202,  203 

,  inclined,  see  Inclined  Belt  Conveyor, 

,  loading,  4,  Chapter  VII 

,  portable,  188,  189 

,  short,  203,  204 

— ,  speeds  of,  148, 151, 152,  153,  154,  155 

,  system  4|  miles  long,  107 

,  typical  arrangements,  4 


321 


322 


INDEX 


Belt  elevator,  Chapter  XIV  and  specific  ref- 
erences below. 

.centrifugal   discharge,  belts  for;   see 

Belts  for  Elevators. 

, ,  boot  for,  208,  210,  215,  217, 

219,.     See  also  Boot. 

, ,  buckets  for,  208,  220,  225;  see 

also  Chapters  XVI  and  XIX. 
, ,  capacities  of,   235,   236,   237, 

247,  269 

, ,  casings  for,  316,  317,  318,  319 

, ,  chokes  in,  236,  246,  261,  270, 

275,  276,  277,  286,  287,  301, 
303,  304 
, ,  discharge   chute,   position  of, 

218,    219,    220,    221,  303, 

310,  311.  320 
, ,  discharge  from,  208,  210,  211, 

214,216,220,221,222,224, 

312 
, ,  driving,   209,   266,   269,   272, 

274,  278,  280 

, ,  driving  at  foot,  210,  283 

, ,  for  grain,  208,  217,  218,  226, 

248,  262,  268,  294,  296,  298, 
300,  302,  303 

, ,  inclined,  208,  215,  306,  307, 

308,  309,  311,  312,  314,  315 

— , .path  of  discharge,  211,  212, 

222,  224 

— , ,  pick-up,   208,  210,  213,   217, 

218,  222,  236;  see  also  Chap- 
ter XXI. 

, ,  size  of  pulleys,  212,  214,  215, 

216,  218,  220,  224,  246,  289, 
303 

, ,  speed  of,  211,  212,  213,  215, 

216,  217,  219,  220,  314 

, ,  spill  at  head,  213,  214,  221, 

222,  224,  237,  254,  269,  307, 
310,311,313 

, ,  tension  devices,  210,  270,  274, 

277,  295,  301,  302,  307;  see 
also  Boots 

— , ,  vertical,   208,  212,   215,   313, 

314 

— ,  continuous  bucket,  207,  210,  240, 
241,  242,  243,  244,  245,  308, 
309 

— , ,  belt  for,  254 ;  see  also  Belts  for 

Elevators 

, ,  buckets    for,    241,    242,   243, 

256,  260 

,  —  — ,  capacities,  243 

— ,  —  — ,  discharge  from,  240,  241 

— , ,  inclination  of,  242,  308,  313 

— , ,  loading,  240,  241,242 

— , ,  path  of  belt,  307,  308,  3b9 

— ,  —  — ,  pulleys,  aize  of,  244 

— , ,  speeds  of,  243,  244 

— , ,  vertical,  208,  314 

,  inclined,  208,  306,  307,  308 

,  — ,  advantages,  313 


Belt  elevator,  inclined  buckets,  spacing  of, 
314 

,  — ,  disadvantages,  315 

,  — ,  inclination  of,  242,  308,  313 

,  —  path  of  belt,  307,  308,  309 

,  —  pick-up,  236,  306 

,  — ,  position  of  chute,  310,  311 

,  — ,  pulleys,  size  of,  311,  313,  314 

,  — ,  speed   of,    243,   244,   310,    312, 

314, 
Belts  for  conveyors  (general  facts) 

,  abrasion  of  11,  12,  18,  19,  26,  133, 

142 

,  accidents  to,  135,  136,  137,  156, 

159,   165,   166,   167,   180,   182, 
187,  196,  197,  199,  200 

,  adherence  of  dirt,  176,  182,  183 

,  cheap,  197 

,  choice  of,  55,  184, 

,  cleaning,  123,  166,  176,  177,  178, 

179,  180 

,  composite,  7 

,  contact,  coefficient  of,   109,  266, 

267,  299 

,  cracking  of,  15,  17,  36 

,  creep  of,  123,  124,  127,  266,  267 

,  curves  in,  130 

,  cutting  of,  11,  118 

,  damaged  by  side-guide  idlers,  13, 

71,  80,  167,  197 

, skirt-boards,  137,  138,  154, 

197 

,  driving,     3,     Chapter     V,     also 

Pulleys 

,  duck  for;  see  Specific  Belts,  also 

Duck 
— ,  endless,  40 

,  fasteners  for,  56,  57,  58,  166 

— ,  feeders  for,    118,   139,    140,    141, 
148 

,  flanged,  7,  43,  44 

— ,  flat,  8,  9,  84,  86,  146,  184 

,  for  grain,  6,  7,  8,  9,  10,  22,  31,  37, 

40, 150 

,  for  packages,  48,  53,  55,  95,  184, 

202,  207 

,  hemp,  2,  64 

— ,  high-speed,  108,  190,  191 

,  hinged  edge,  17,  44 

,  leather,  2,  7 

— ,  life  of,  31,  44,  120,  196,  197,  200 

— , ,  rule  for,  196 

— ,  narrow,  13,  152 

— ,  old,  197 

— ,  on  flared  idlers,  83,  91,  146 

,  Plummer's,  17,  19 

,  protecting,  3,  177,  178,  179,  180, 

181,  182,  183 

,  Ridgway's,  17 

— ,  running  crooked,  8,  16,  77,  78,  79, 
167 

,  Selleck's,  17 

,  strength  of,  39,  52,  53,  54 


INDEX 


323 


Belts  for  conveyors,  supports   for,  2,    16, 

95;    see  also  Idlers  „ 

— ,  tensions,  109,  110,  111,  112,  113 

,  thickness  of,  41,  108,  110,  114,  115^ 

,  to  make  run  straight,  7*9,  80,  81 

,  ultimate     strengths,      111;       see 

Specific  Belts 

,  vanner,  43 

— ,  width    of,    113,    114,    152;     see 

Capacities,  Chapter  VII 
Belts  for  conveyors  (varieties  of) 
— ,  balata,  2,  49,  50,  51,  54,  190,  199 
— ,  — ,  duck  for,  50 
— ,  — ,  flexibility  of,  50,  55,  56 
— ,  — ,  strength  of,  54 
— ,  — ,  weight  of,  51 
— ,  rubber,    2,    Chapter    II,    Chapter    III 

and  specific  references  below 
— ,  — ,  aging  of,  22,  23,  29,  32,  36,  38,  44, 

197,  205 

— ,  — ,  assembly  of,  2,  20,  21,  24,  25,  35,  41 
— ,  — ,  Bowers',  19 
— ,  — ,  "  competition,"  37 
— ,  — ,  duck  for,  20,  22,  31,  37,  53 
— ,  — ,  edge  construction,  24,  25 
— ,  — ,  flexibility  of,  12,  17,  47,  48,  50,  55, 

74,  75,  76,  81 

— ,  — ,  friction  surface,  2,  22,  185 
— ,  — ,  idlers  for;   see  Idlers 
— ,  — ,  lamina  construction,  24 
— ,  — ,  reinforced  covers,  12,  24,  25,  29,  30 
— ,  — ,  —  by  metal,  19 
— ,  — ,  rubber  covered,  12,  22,  24,  26,  27, 

29,  30,  38,  41,  52,  185,  197,  199 
— ,  — ,  stepped-ply,  12,  15,  16,  24,  29,  76 
— ,  — ,  stitched,  23 
— ,  — ,  straight-ply,  16,  22 
— ,  — ,  strength  of,  53,  54,  111 
— ,  — ,  Robins',  12 
— ,  — ,  Voorhees,  19 
— ,  — ,  vulcanizing,  21,  44,  59 
— ,  — ,  weight  of,  41,  42 
— ,  solid-woven,  2,  50,  51,  54,  201 
— ,  stitched    canvas,  2,  17,  19,  46,  47,  54, 
129,  200,  205 

— , ,  duck  for,  46 

— , ,  flexibility  of,  47,  48,  49,  55,  66, 

81,  82,  184 

— , ,  saturating  compounds  for,  47,  48, 

184,  201,  255,  275 

— , ,  strength  of,  54 

— , ,  weight  of,  49 

Belts  for  elevators  (general  facts) 

,  abrasion  at  feed  point,  288 

-  — ,  accidents,  227,  236,  243,  250,  261, 
262,  275,  281,  288,  290 

,  choice  of,  252,  254,  255 

,  contact,  coefficient  of,  252,  266, 

267,  299 

,  creep  of,  250,  276,  280 

,  driving,  Chapter  XX 

,  fasteners  for,  58,  263,  264,  265 

,  for  grain,  31,  32,  37,  38,  247 


Belts  for  elevators,  injured  by  slip,  236,  246, 

249,  250,  253,  275,  276,  277,  302, 

304 
,  injuries  to,  236,  246,  249,  250,  252, 

260,  275,  277,  288,  290 

,  leather,  209,  247 

,  protecting,  253,  257,  258,  260, 261, 

290 

,  punching  for  bolts,  259,  260,  261 

— ,  strength  of,  39,  52,  53,  54 

,  stresses,  allowable,    246,  274,  310 

,  tensions,  calculation  of,  271,  272, 

273,  274,  275,  306,  309,  310 

,  thickness,  248,  274,  275 

,  wear  of,  249,  250 

,  width  of,  252,  255,  261 

,  wire  mesh,  209 

,  wire  rope,  209 

Belts  for  elevators,  (varieties  of) 

,  balata,  49,  50,  209,  255 

,  rubber,  2,  18,  19,  10  to  46  inclu- 
sive, 209,  247,  248,  251,  253,  254 

,  — ,  duck  for,  22,  46,  248,  252.  254 

,  — ,  friction-surface,    2,    22,    185, 

248,  249,  251,  252 

,  — ,  rubber-covered,  248,  249,  250, 

251,  252,  253,  260 

,  solid- woven,  50,  51,  52,  208 

,  stitched    canvas,  46,  47,  48,  49, 

254,  275 

Bemis  belt  cleaner,  180 
Bird,  W.  W.,  276 
Blaisdell  devices,  171,  172 
Blisters  on  belt,  26,  32,  40,  59,  166,  252 
Boiler-houses,  distributing  coal  in,  202 
Bolts  for  buckets,  240,  243,  250,  256,  257, 

258,  275,  289 

,  pull  on,  258,  263,  289 

lagging,  250,  268,  275,  278,  302 

Books,  belt  conveyor  for,  184 

Boot,  automatic  take-up,  300,  301 

— ,  cast-iron,  295,  296 

— ,  concrete,  281 

— ,  digging  from,  208,  210,  213,  215,  269, 

270,  272,  273,  282,  283,  286,  287 
— .  double-sided,  283 
— ,  dust-tight,  284 
— ,  fixed-bearing,  281,  282,  283 
— ,  for  coal,  219,  220,  283,  284, 
— ,  —  grain,  217,  222,  283,  294,  295,  296, 

297 

— ,  —  wet  ore,  285 
— ,  pick-up  from,  272,  273 
— ,  shape  of  bottom,  273,  282,  286,  287 
— ,  sloped-front,  215,  219,  283,  284,  286, 289 
— ,  steel,  293,  295 
— ,  take-up,  281,  284,  286,  287,  295 
— ,  wood,  294 
Boss  pulley,  291 
Bottle-caps,  belt  for,  192 
Box-car  loader,  190 
Boxes,  belt  conveyor  for,  184 
Boxes,  elevator  for,  320 


324 


INDEX 


Brake,  for  elevator,  305 

Bran,  elevating,  218 

Brass-nuts  in  boots,  285 

Bristol  Co.,  56 

Brotz  discharge  device,  160 

Brown,  Dr.,  H.  H.,  302 

Brushes  for  belts,  123,  166,  176,  178,  179 

Bucket,  capacity  of,  208,  220,  222,  230,  231, 

232,  233,  234,  235,  236,  243 

— ,  continuous,  241,  242,  243,  256,  260 

— ,  European,  237,  239,  258 

— ,  fastening  to  belt,  256,  257,  259,  260,  261 

— ,  for  liquids  and  pulps,  232,  238 

— ,  malleable-iron,  209,  225,  230,  231,  232, 

233,  234,  235,  257 

— ,  Manufacturers'  Standard,  230 

— ,  punching  for  bolts,  242,  256,  259,  260 

— ,  round-bottom,  208,  225 

— ,  seamless,  209,  230 

— ,  sheet-steel,  208,  225,  228,  229,  251 

— ,  Style  A,  225,  230,  231 

— ,  Style  AA,  225,  230,  231,  232 

— ,  Style  B,  225,  230,  231,  233,  235 

— ,  Style  C,  225,  232,  233,  235 

— ,  tearing  loose,  227,  236,  243,  250,  261, 

262,  281 

— ,  triangular,  208,  226,  239 
— ,  two-piece,  209,  239 
"  Buffalo  "  bucket,  225,  228,  258 
Buffalo,  first  elevator  at,  247 
Bureau  of  Standards,  27,  32,  35,  44 
Butt-strap  joints,  264,  265 
By-product  coke  plants,  204 


"  C  "  bucket,  225,  232,  233,  235 

,  pick-up  of,  235 

Calculation  of  stress  in  elevator  belt,  271, 

272,  273,  274,  275,  308,  309,  310 
Caldwell,  H.  W.  &  Son  Co.,  150 
Canneries,  belts  for,  48,  55,  199 
Cans,  conveyor  for,  193 
— ,  elevator  for,  193 
Canton  No.  1  Elevator,  8,  162 
Capacity  of  buckets;    see  Bucket,  capac- 
ity of, 

belts,  flat,  84,  86,  146 

,  hourly,  148 

,  on  flared  idlers,  83,  146 

,  inclined,  148,  154 

,  package  conveyor,  187 

,  peak-load,  148 

,  troughed,  143,  144,  147,  149 

elevators,  235,  236,  237,  243,  247,  269 

,  peak-load,  235,  236 

Car  loaders,  172,  190 

Carr  belt  cleaner,  180 

Casings  for  elevators,  316,  317,  318,  319 

Catenary  curve  of  elevator  belt,  307 

Cement  clinker  conveyor,  83 

Cement  elevating,  218 

Centrifugal  discharge;    see  Belt  Elevator, 

centrifugal  discharge 


Centrifugal  force,  21 1 
Chaff,  elevating,  218 

Chain  conveyors  compared  with  belt  con- 
veyors, 205 

Chemicals,  elevators  for,  219,  281 
Chicago  Post  Office,  mail-conveyors,  129 
Chips,  conveyors  for,  204 
Choice  of  conveyor  belts,  55,  184 
—  elevator  belts,  252,  254,  255 
Chokes;   causes  of,  301,  302 
— ,  in  discharge  chutes  of  conveyors,  156, 

197 
— ,  in  elevators,  236,  246,  261,  270,  275,  276, 

277,  286,  287,  301,  303,  304 
— ,  prevention  of,  303 
Chutes,  discharge,  for  belt  conveyor,  156 

— ,  — , ,  tripper,  156 

— ,  — ,  for  elevators,  207 

— , — , — — .position    of,    218,    219,    220, 

221,  303,  310,  311,  320 
— ,  feed,  for  elevators,  210,  217,  218,  219, 
286,  287,  288 

— ,  — , ,  chokes  in,  217,  286,  287 

— ,  loading,  belt  conveyor,   113,   133,  134, 
140 

— ,  — , ,  drip,  136,  137 

— ,  — , ,  finger-bar,  135 

— ,  — , ,  run-of-mine  coal,  135 

— ,  — , ,  screen,  135,  136 

— ,  — , ,  side-delivery,  203 

— ,  — , ,  transfer,  136 

— ,  — ,  for  continuous  buckets,  208,  241 

— ,  tripper,  166 

Cider-press  cloth,  24,  30 

Cinders,  elevator  for,  215,  219 

Clay  conveyor,  6 

Cleaning  conveyor  belt,  123,  166,  176,  177, 

178,  179,  180 

,  accessibility   for,    177,    181,    182, 

183 

—  pulley  rims,  122,  180 
Cleanout  doors,  261,  295,  318 
Clearance  in  boot,  283,  286,  287 
Cleats  on  belt,  142,  188,  246,  320 

Coal,  conveyor  for  run-of-mine,  92,  93,  107, 

172,  173 

— ,  elevator,  215,  219 
Coefficients  of  belt  contact,  109,  252,  266, 

267,  299 
Coke  conveyor,  belts  for,  204 

,  belt  record,  129,  198 

,  idlers  for,  77 

,  spill  on  return  run,  181 

—  elevator,  219,  282 
Cole,  David,  291 

Comparative  capacities  of  elevator  buckets, 

230,  269 

Comparison  between  belt  conveyor  and  car- 
haulage,  107 

flight  conveyor,  203 

Compensating  gear  drive,  126 
"  Competition"  belts,  37 
Complaints  about  belts,  196 


INDEX 


325 


Composite  belt,  7 

Compounding  of  rubber,  21,  22 

Compounds  for  saturating  canvas 
47,  48,  184,  201,  255,  275  * 

Concentrators,  7,  9,  10,  11,  91,  141 

Concrete  boot  and  pit,  281 

Concrete,  cleaning  belts  from,  180 

Conveying  Weigher  Co.,  56 

Cook  reinforced  belt,  19 

Cookman-Neall  tripper,  161 

Cory  and  Dandridge  reinforced  belt,  19 

Cost  of  conveying  material,  198,  199,  201, 
203 

elevating  material,  249,  251,  252 

Covers  for  conveyor  belts.  12,  19,  21,  22,  24, 
26,27,29,38,41,52,185,197, 
199  (see  also  Belts  for  Con- 
veyors; Rubber) 

,  quality  of,  27,  29,  30,  38,  40, 

197,  199 

,  reinforced,  12, 19,  24,  25, 29, 30 

,  tearing  of,  30,  197,  199 

,  thickness  of,  22,  24,  26,  38,  41 

—  elevator  belts,  248,  249,  250,  251 

Cowley  patent  belt,  192 

Cracking  of  belts,  15,  17,  36 

Creep  of  belt,  123,  124,  127,  250,  276,  280 

Crescent  Belt  Fastener  Co.,  56 

Crooked  running  of  conveyor  belt,  16,  77, 
78,  79,  167 

Crown  of  pulley  rims,  128,  261,  279,  292 

Curing  or  vulcanizing,  21,  44 

Curved  backs  of  buckets,  225,  228,  258,  262 

Curves  in  belt  conveyor,  130 

Cutting  of  belts,  11,  118 

D 

Damage  to  belt  from  buckets,  260 

Dart,  Joseph,  247 

Dead  material  in  boot,  286 

Deck,  protective,  180,  181,  182,  183 

Deflection  of  down  run  of  elevator  belt,  308 

Deflector  pulley,  129,  130,  180 

,  scraper  for,  180 

Department  stores,  belts  for,  184,  185,  186, 

187 

Depressed  loading  end,  138,  169,  171 
Deterioration  of  belt  in  storage,  205 

rubber,  22,  23,  29,  32,  36,  38,  44,  197, 

205 

Dick  Co.,  R.  &  J.,  51 
Digging  from  boot,  power  required,  269 
Dirt,  adherence  of,  120,  122,  123,  128,  176, 

182,  183 

— ,  effect  of,  on  belt  contact,  268 
Disadvantages  of  belt  conveyor,  205 

other  conveyors,  204,  205 

Discharge   from   conveyor   belt,    increased 
range  of,  171 

,  near  loading  end,  169,  203 

,  over  end  pulley,  156,  157,  176 

,  partial,  by  plow,  6,  158,  160 

,  photographs  of,  157 


Discharge  from  conveyor  belt  through  trip- 
per, 7,  140,  Chapter  VIII 
Discharge  from  elevator,  centrifugal,  207, 

208,  211 
,  continuous  bucket,  207,  208,  240, 

241,  244 

,  delayed,  221 

,  factors  which  govern,  210,  241, 

244 

,  photographs  of,  223 

,  where  it  begins,  224,  312 

Dish-pan  idler,  9,  69, 
Distributing  by  plows,  158,  160 
tripper,  159,  161,  162 

—  coal  in  boiler-houses,  202 
ships,  190 

Dodge,  James  M.,  tripper  extension,  172 
Dodge,  Oren  C.,  inventor  of  tripper,  7 
Doors  in  casing,  318 
Double  belts,  192 

—  row  of  buckets,  262,  280 

Down  run  of  elevator  belt,  path  of,  307 

Dribble  at  head  of  elevator,  240,  244 

— ,  on  return  run,  177,  182,  183 

— ,  over  end  pulleys,  156,  157,  158,  176 

Drip  chute,  136,  137,  158 

Drive  of  belt  conveyor,  96 

,  at  foot,  118,  121 

by  compensating  gearing,  126 

—  by  pressure  belt,  13,  124,  125 
-  by  tandem  pulleys,   119,   120, 
121,  122 

by  three  pulleys,  127 

,  proper  place,  118,  121 

—  elevator,  266,  272,  273,  274 
Driving  contact,    coefficient  of,   109,   110, 

252,  266,  267,  269 
Drying  machine  apron,  62 
Duck  for  balata  belt,  50 

elevator  belt,  22,  248,  252,  254 

rubber  belt,  20,  22,  31,  37,  46,  53,  248, 

252,  254 

stitched  canvas  belt,  46 

— ,  splices  in,  36,  37,  40,  41,  76 

— ,  tests  of,  33,  37, 

Duluth,  belt  conveyors  at,  7,  162 

Durability  of  belts,  22,  55,  200;    see  also 

Life  of  Belts. 
Duryea  Mfg.  Co.,  52 
Dust,  effect  on  belt  contact,  268,  270 
— ,  explosions,  302 
Dust-tight  boots,  284 

casings,  318 

Dusty  material,  speed  of  elevator  for,  218 

E 

Early  grain  elevators,  247 

—  history  of  belt  conveyor,  6,  7 
Economical  life  of  belt,  55,  200 
Edges  of  rubber  belts,  24,  25 

,  thick,  13,  24,  25 

Edge  wear,  23,  24,  167,  199 


326 


INDEX 


Edison  cement  plant,  43,  140,  1 60 

—  feeder,  140 

— ,  New  Jersey,  belt  conveyors  at,  10 
Edmond  automatic  boot  take-up,  295,  301 
Efficiency  of  elevator  drive,  269,  271,  273 
Elevating     capacity     distinguished     from 

bucket  capacity,  236,  247 
Elevator;   see  Belt  Elevator. 
Elevator  belt;   see  Belts  for  Elevators. 
Elevators  at  Lake  ports,  247 
— ,  capacity  of;    see  Buckets,  capacity  of, 

also,  Belt  Elevators,  capacity  of 
— ,  grain,  7,  8,  9,  10,  14,  32,  38,  208,  217, 

218,  226,  248,  262,  268,  294,  296,  298, 

300,  302,  303 

—  instead  of  belt  conveyors,  204 
"  Empire"  bucket,  225,  230 
Enclosures  for  belt  conveyor,  181,  182,  183 
Endless  belt,  40,  59 

European  buckets,  237,  239,  258 
Evans,  Oliver,  6,  247,  258 
Excavated  earth,  belt  for,  204 
Excess  of  belt  capacity,  116,  148 

bucket  capacity,  235,  236,  237,  247 

Excessive  speed  of  conveyor  belt,  118,  197 

elevator  belt,  213,  226,  251 

Explosion  caused  by  choke,  276,  302 
External  wear  of  belt,  249,  250 


Fasteners  for  conveyor  belt  joints,  56,  57, 
58 

coming  loose,  166 

—  elevator  belt  joints,  58,  251,  264 
Faulty  design  of  belt  conveyor,  117 
enclosures,  183 

—  drive  for  belt  conveyor,  1 19 

—  formula  for  horse-power,  112 
"  Favorite  "  bucket,  225 
Feed,  intermittent,  141,  148 

Feed  into  boot,  213,  215,  217,  218,  219,  236, 

286,  288 
Feeders,  Edison,  140 

—  for  belt  conveyor,  118,  139,  140,  141,  152 
— ,  Reinecke,  140 

— ,  Stuart,  140 

Feeding  hopper,  141 

Feeding,  related  to  capacity  of  conveyor, 

139,  152 

Fertilizer,  elevator  for,  219,  281 
Filler  threads,  20,  46,  47,  50,  56 
Filling  of  bucket,  imperfect,  217,  269 

,  improved,  306 

Fine,  dry  material,  belt  speed  for,  218 
Fire  caused  by  choke,  276,  301 

hot  bearing,  294 

First  discharge  point  in  belt  conveyor,  169, 

203 

Five-pulley  idler,  16,  68,  76,  77,  93 
Fixed  tripper,  7   160;   see  also  Tripper, 

,  objections  to,  140,  160,  161,  197 

—  with  movable  pulley,  161 


Flanged  belt,  7,  43,  44 

—  pulleys,  280,  291,  292 
Flapper  for  cleaning  belt,  179 
Flared  idlers,  83,  91,  146 

,  Capacity  of  belt  on,  146 

Flat  belt,  8,  9,  84,  86,  146,  184 

— ,  capacity  of,  84,  86,  146,  187 
Flexibility  of  balata  belt,  50,  55,  56 

rubber  belt,  12,  17,  47,  48,  50,  55,  74, 

75,  76,  81,  253 

stitched  canvas  belt,  47,  48,  49,  55, 

66,  81,  82,  184 

thick  belt,  253 

Flexible  Steel  Lacing  Co.,  57 
Flight  conveyor  compared  with  belt  con- 
veyor, 203,  204 
Floating  ply,  29 
Flour,  buckets  for,  228,  239 
— ,  speed  for  elevating,  218 
Fly-feed,  288 
Folsom  belt,  19 

Food  products,  elevator  for,  281 
Foot  of  belt  conveyor,  drive  at,  118,  119 

,  elevation  of  pulley  rim,  71,  72 

elevator,  drive  at,  210,  283 

,  losses  at,  271,  273 

Foot  pulley  of  elevator,  material  catching 
at,  290,  292 

,  size  of,  214,  216,  236,  289 

,  too  small,  214,  216,  218,  236, 

289,  303 

Foot  wheel,  elevator  without  a,  291 
Four-pulley  idler,  14,  16,  68 
Free-flowing  materials,  215 
Friction,  belt-,  coefficient  of,  109,  110,  252, 

266,  267,  268,  269 
— ,  compound,  20,  22,  23,  25,  53,  '248,  253 

,  low-grade,  248 

,  strength  of,  30,  31,  34,  35,  36,  38,  40, 

53,  248 

—  of  material  in  bucket,  221 
Irlccion-surface  belt,  2,  22,  185,  248,  249, 

251,  252 

Front-feed  into  grain  boot,  217 
Full-load   cross-section   on   conveyor   belt, 
146,  152 

G 

Gap  between  elevator  belt  and  bucket,  240, 

243,  256,  260 

between  idler  pulleys,  14,  197 

Gemlo  back-stop,  305 

Gilsonite  for  canvas  belts,  48 

Girard  Point  Elevator,  31,  248 

Goodrich  Rubl>er  Co.,  B.  F.,  25,  42,  43,  46, 

76,  99,  151,  253,  254 
Goodyear  Tire  and  Rubber  Co.,  25,  33,  39, 

41,99 

Grab  test,  for  belt  duck,  33,  39 
Grain  conveyor  belt,  6,  7,  8,  9,  10,  22,  31,  37, 

40,' 150 

— ,  capacity  of,  150,  151 
,  early  r  6,  7 


INDEX 


327 


Grain  conveyor,  horse-power  of,  99       M 

,  method  of  loading,  151 

speeds,  154 

Grain  elevator,  7,  8,  9,  10,  14,  32,  38,  %8, 
212,  217,  218,  226,  248,  262,  268, 
294,  296,  298,  300,  302,  303 

belt,  31,  32,  37,  38,  247 

buckets,  225,  226,  227,  228,  229,  237, 

239,  258 

,  speeds  for,  212,  216,  217 

Gravel,  belts  for,  201,  204 

Gravity  take-up,  131 

Grease  lubrication,  65,  68,  86,  87,  94,  97, 
297 

Griscom  bucket  fastener,  258 

Guards  over  foot  pulley,  290 

Gulf,  Florida  and  Alabama  R.  R.,  173 

Gutta-percha  cover,  50 


II 

Haddock,   Edwin  J.,  experiments  of,   127, 

268 
Handling,  belts  injured  in,  199 

—  materials,  cost  of,  198,  199,  201,  203,  249, 

251,  252 
Hanffstengel's    experiment    with    elevator 

boot,  272 
Haulage,    compared    with    belt    conveyor 

system,  107 
Heat,  belts  to  resist,  23,  48,  199 

—  due  to  slip,  275 

—  effect  on  rubber,  44,  46,  197,  199 

— ,  injures  belts,  23,  48,  50,  197,  199,  275, 

276,  302 

Heaton  reinforced  belt,  19 
Hegeler  and  Holmes  drive,  126 
Height  of  continuous  bucket,  243 
Helical  idlers,  18 
Heyl  and  Patterson,  Inc.,  171 
"  High-Duty  "  belt  fastener,  58 
High-speed  elevator,  212,  213 

,  for  conveyors,  108,  190,  191 

,  limitations  of,  213,  218,  226 

Hinged-edge  belt,  17,  44 
Hohl  and  Schorr  belt,  19 
Hopkins  and  Fellows  elevator,  193 
Hopper,  choke  in  feed,  217 
— ,  loading,  140 

Horizontal  loading  end  for  inclined  belt,  154 
Horse-power    of    belt    conveyer,    approxi- 
mate rule,  98 

,  calculation  of,  96 

,  compared  with  h.p.  for  other 

conveyors,  203,  205 

,  comparison  of  rules,  100 

with  improved    idlers,  92,   93, 

10G 

elevator,  calculation  of,  271,  272, 

273,  274 

Horse-power  pull,  108 

Horse-power  tables,  100,  101,  102,  103,  104, 
105 


Hot  bearings,  294,  298 

,  signal  system  for,  298 

Hourly  capacities,  148 

Housing  over  belt  conveyor,  181,  182,  183 

Howard  patent  idler,  67 

Hoy  conveyor  drive,  126 

Hugo,  T.  W.,  7,  162 

Humphreys  tripper,  167 

Humps,  idlers  at,  70,  74 

— ,  pulleys  at,  71,  73 

— ,  skirt-boards  at,  138 

Hyatt  roller  bearing,  90,  91 

I 

Idler,  ball-bearing,  89,  90,  92,  94,  98 
• — ,  — ,  horse-power  formula  for,  106 
— ,  five-pulley,  16,  68,  76,  77,  93,  145 
— ,  — ,  defects  of,  68,  76 
— ,  flared,  83,  91,  146 
—  for  balata  belts,  55,  66 

picking  belt,  67,  193 

stitched  canvas  belt,  55,  66,  71,  82 

— ,  four-pulley,  14,  16,  68 

— ,  grease  lubrication  for,  65,  66,  68,  86,  87, 

94,97 

— ,  helical,  18 
— ,  improved,  savings  due  to,  92,  93,  106, 

107,  108 
— ,  I  ynch,  16 
— ,  Mann  and  Neemes,  18 
— ,  multiple-pulley,  16 
— ,  oil  lubrication  for,  13,  87,  88,  91,  94 
— ,  Peck,  16 
— ,  Plummer,  16 
— ,  Proal,  18 
— ,  pulleys  for,  broken  rims,  197 

— , ,  chilled  rim?,  77 

— , ,  gaps  between,  14,  197 

— , ,  sheet-steel,  88,  90,  91 

— , ,  wear  of,  68,  77,  177,  197 

— ,  return,  69,  70 

— ,  — ,  setting  of  to  shed  dirt,  177 

— ,  Robins,  13,  14,  16 

— ,  roller-bearing,  90,  91,  92,  93,  94,  95 

,  horse-power  formula  for,  106 

— ,  Rouse,  18 

— ,  side  guide,  8,  13,  69,  70,  71,  80, 167, 177 

— ,  — ,  belt  damaged  by,  13,  71,  80,  167, 197 

— ,  simplicity  of  construction,  86,  88 

— ,  single  plane,  67 

— ,  tapered  roller  bearing,  85 

— ,  Thomas,  18, 

— ,  three-pulley,  11,  13,  65,  66,  67,  76,  77, 

82 

— ,  tilting,  160 
— ,  two-plane,  11,  65,  66 
— ,  two-pulley,  68 
— ,  Uniroll,  84,  85,  91,  146 
— ,  Vrooman,  18 
Idlers,  spacing  of,  69,  72,  73 
— ,  spool,  8,  11,  69,  83 
• — ,  steering  effect  of,  16,  78,  79 


328 


INDEX 


Impact  at  loading  point,  133 
Imperial  Belting  Co.,  184,  201 
Impregnating  canvas  belt,  47,  48,  184,  201, 

255,  275 

Improvements  in  rubber  belt,  22,  37,  41,  44, 

292  j 

Inclined  belt  conveyor,  angle  of,  115,  135, 

142,  148 

— ,  capacity  of,  145,  148,  154 
— ,  horse-power  of,  97,  98,  104,  105 
— ,  loading,  115,  116,  135,  137,  141, 

154 
— ,  pull  due  to  incline,  97,  112,  113, 

121 

— ,  skirt-boards  for,  137 
— ,  special  belts  for,  143 
— ,  speed  of,  115,  116,  148,  154 
Inclined  belt  elevator,  208,  306,  307,  308 
— ,  advantages  of,  313 

,  bucket  spacing,  314 

,  disadvantages  of,  315 

—  — ,  inclination  of,  308,  313 

,  path  of  belt,  307,  308,  309 

— ,  pick-up,  236,  306 
— ,  position  of  chute,  310,  311 
Injuries  to  elevator  belts,  227,  236,  246,  250, 
253,  255,  256,  260,  261,  263,  275,  276,  277, 
281,  302,  304 
Inspection  of  belt,  177,  182,  183,  252,  263 

buckets,  261 

Insufficient  speed  of  continuous  buckets, 

215 
Intermittent  feed  to  conveyor,  142,  148 

elevator,  235,  237 

Internal  wear  of  belt,  249 
International  Conveyor  Corporation,  172 
Irregular  supply  of  material,  effect  of,  142, 
148,  235,  237 


Jackson  belt  fastener,  58,  264 

Jeffrey  Mfg.  Co.,  65,  156,  160,  165,  283 

Joining  ends  of  belt,  56,  57,  58,  263,  264, 

265 
Joints,  vulcanized,  59 

K 

Keeping  rubber  goods,  46 


Lagging,  120 

— ,  bolts  for,  122,  250,  268,  275,  278,  302 

—  elevator  head  pulley,  268,  270 

—  tandem  pulleys,  121 

— ,  wear  of,  120, 122,  236,  250,  268, 275,  277, 

278,  302 

Lamina  belt,  24,  35 
Lamson  Co.,  129,  185,  186,  192 
Lap-joint  in  elevator  belt,  263 
Large  foot  wheel,  good  effect  of,  219 

—  tandem  drive,  120 
Lewis,  Wilfred,  267,  276 


Life  of  belts,  31,  44,  55,  120,  196,  197,  200, 
251,  252 

,  "  Rule  "  for,  196 

Light,  effect  of,  on  rubber,  44,  46 
Lime,  pulverized,  elevating,  218 
Limestone,  belt  conveyor  for,  84  166,  117 
Link-Belt  Company,  84,  85,  99,   124,  164, 

186,  187,  190 

Liquids,  elevator  for,  220,  237 
Liverpool,  grain  conveying,  at,  7,  8 
Load,  disturbance  of,  on  45°  idlers,  15 
— ,  full  cross-section  desirable,  146,  152 

—  on  troughed  belt,  144,  146,  152 
Loader,  mechanical,  for  elevator,  210 
Loading  chutes,  113,  133,  134,  140,  154,  197, 

203 

—  end,  depressed,  138,  169,  171 
,  horizontal,  154 

—  hoppers,  140,  141 

—  into  elevator  buckets,  210,  240,  245,  273 

—  leg,  243,  273 

Long  conveyors,  203,  205 

—  distance  belt  conveying,  107,  108 
Lower  run  of  belt  conveyor,  dirt  on,  176, 

177,  182,  183, 

Lubrication  of  boots,  284,  293,  296 
idlers,  83,  85,  86,  88,  90,  91,  92,  182, 

183,  185,  186,  197 
,  accessibility  for,  83,  84,  87,  88,  94, 

181,  182,  183 

by  grease,  65,  66,  68,  86,  87,  94,  97 

oil,  13,  87,  88,  91,  94 

Luther  double  belt,  192 
Lynch  idler,  16 
Lyster,  G.  F.  7,  134 


M 

Macdonald,  James  A.,  14 
Main  Belting  Co.,  66,  71,  99 
Malleable-iron  buckets,  209,  225,  230,  231, 

232,  233 

Man  elevator,  319 
Manierre  box-car  loader,  172,  190 
Mann  and  Neemes  idler,  18 
Manning  reinforced  belt,  19 
Manufacturers'  Standard  Buckets,  230 
Marine  leg,  289 
Mason  idler,  80 
Maximum  belt  tension,  274 
—  load  on  troughed  belt,  144 
Maximum   and   minimum   plies   for   belts, 
115,  275 

speeds  for  belt  conveyors,  153 

Merrick  and  Sons,  7 

Messiter  tripper,  168 

Metal  reinforcement  for  conveyor  belts,  19 

Metcalf's  specifications  for  grain  belts,  31, 

32,  248 
,  comment  on,  32,  33,  34,  35, 

36,  37 

Metzler  edge  for  rubber  belt,  24 
Miller's  Guide,  6 


INDEX 


329 


Mill-products  (bran,  chaff,  etc.)  elevating, 

218 

Mineral  coating  for  canvas  belt,  48        £ 
Minerals,  elevators  for,  215,  ^19 
Minimum  number  of  plies  in  elevator  belt, 

275 

"  Minneapolis  "  bucket,  226,  227,  228,  229 
Moisture  in  duck,  correction  for,  34 
— ,  absorption  of,  by  belts,  55,  56,  184,  248, 

249,  252,  253 
Morton  tripper,  168 
Moss  tripper  device,  171 
Moulton  and  Son,  John  T.,  8,  14 
— ,  George  M.,  162 

N 

Narrow  belts,  13,  86 

Natural  troughing,  68,  74,  75,  76 

Neall,  Samuel  W.,  30 

New  Jersey  and  Pennsylvania  Concentrat- 
ing Co.,  10 

New  Mexico,  concentrator  in,  elevators  at, 
232,  238 

Newspaper  elevator  and  conveyor,  192 


O 

Oil  lubrication  (boots)  296,  297 

-  (idlers),  13,  87,  88,  91,  94,  186 
Oilless  bearings  for  boot,  293 

package  conveyors,  185 

Open  pile,  digging  from,  236 
Operating  conditions  affecting  capacity  of 
conveyor,  145,  148 

elevator,  235,  236,  237, 

Ore  conveying,  11,  12,  29r  204 
Ore  elevators,  251,  252,  291 
Overcure  of  belt  in  vulcanizing,  44 
Overload  capacity  of  conveyors,  144,  148, 
150,  152 

elevators,  235,  236 

Overload  release,  276,  304 

Overloads  on  elevator  belts,  247;   see  also 

Chokes 
Overstretching  belts  in  manufacture,  40 


Package  conveyor,  184,  185,  186,  187 

,  belts  for,  48,  53,  55,  95,  184,  202,  204 

Pads  behind  elevator  buckets,  253,  257,  258, 
260,  261 

Page  auxiliary  drive  for  belt  conveyor,  126 

Palmer's  tilting  idler,  160 

Para  rubber,  21,  22,  34 

Parabolic  curve  of  elevator  belt,  308,  309 

Path  of  discharge  from  elevator  buckets, 
212,  213,  214 

down-run  of  elevator  belt,  307 

Pattee  reinforced  belt,  19,  63 

Peak  load  capacity,  148,  235;  see  also  Over- 
load Capacity 


Pennsylvania  R.  R.  Co.,  248 
Perkins  newspaper  elevator,  192 
Photographs  of  conveyor  discharge,  157 

elevator  discharge,  223 

Picking  belts,  193,  194,  195 

,  idler  for,  67,  193 

Pick-up  of  elevator  buckets,  211,  289,  306 

,  bad,  due  to  small  pulley,  289,  303 

of  coarse  material,  215,  216,  219,  235, 

282,  289 

grain,  213,  217,  235,  269 

,  pull  in  belt,  due  to,  271,  272,  273 

Piez  pressure-belt  drive,  13,  124,  125 

Plantation  rubber,  21,  22,  34 

Plies  of  belt  fabric;   see  Assembly  of  Belt. 

,  coming  apart,  11,  23,  24,  32, 

159,  197,  199,  246,  248 

,  number  of,  in  conveyor  belt, 

108,  109,  110,  115 

, ,  —  elevator,    248,    274, 

275 

Plow  for  discharging  from  belt,  6,  158,  ICO 
— ,  traveling,  159 
Rummer  belts,  17,  19,  95 

—  idler,  16,  75 
Portable  conveyors,  188 
Portable  Machinery  Co.,  188 

Power,  for  various  conveyors,  comparisons 

of,  203,  205 
— ,  waste  of,  in  elevator  boot,  215,  218,  289, 

303 
Pratt  loader,  190 

—  rubber  belt,  41 

Pressure  in  buckets  at  head  of  elevator,  211, 
213,  214,  217,  220,  306 

foot  of  elevator,  211,  213,  214, 

215,  217,  220,  306 

Pressure-belt  drive,  13,  124,  125 

Proal  idler,  18 

—  tripper,  168 

Protecting  conveyor  belt,  3,  177,  178,  179, 
180,  181,  182,  183 

—  elevator  belt,  253,  257,  258,  260,  261,  290 
Protective  deck,  180,  181,  182,  183 

—  devices  for  elevators,  276,  298,  304,  305 
Pull,  at  drive  of  belt  conveyor,  108,  109,  110 
— ,  —  head  of  elevator,  269 

—  due  to  pick-up,  271,  272,  273 

—  on  bucket-bolts,  258,  263,  289 
Pulleys  for  belt  conveyors,  3,  96 

at  hump,  71,  73,  130 

,  deflector,  129,  130,  180 

r,  discharge  at,  156,  157,  158,  176 

,  idler,  see  Idlers. 

,  in  trippers,  165,  167 

-  — ,  rims,  dirt  on,  122,  180 

,  — ,  drilling,  123 

,  — ,  elevation  of,  with  respect 

to  idlers,  71  72 

,  — ,  wear  of,  122 

— ,  — ,  width  of,  128 
— ,  size  of,  127,  129,  165 
,  snub,  117,  127,  128,  129,  180 


330 


INDEX 


Pulleys  for  belt  conveyors  elevators,  diam- 
eter at  foot,  214,  216, 
218,  257,  289,  292,  303 

, head,  224,  257,  266,  310, 

311 

,  — ,  related  to  belt  speed,  266 

,  — , bucket  size,  243 

,  face  of,  279 

,  flanged,  280 

,  loose  in  boot,  293 

,  rim  thickness,  279,  280,  292 

,  rough  rim,  277 

,  slat  rim,  277 

,  split,  278 

,  tightening,  278 

,  wear  of,  280,  292 

Pulp,  mineral,  elevator  for,  221,  252,  314 

Punching  belt  for  bolts,  259,  260,  261 

Q 
Quality  of  rubber  covers,  27,  29,  30,  38,  40, 

197,  199 
Quiet  operation,  1,  153,  203 

R 

Radius  of  curvature  of  bend,  130 

Ratio  of  belt  tensions,  108,  109,  110,  277, 
299,  300 

pulley  diameter  to  plies  of  belt,  127, 

165,  266,  268,  289 

Reaney,  William  B.,  162,  167 

Reduced  speed  for  inclined  belt  conveyor, 
154 

Reinecke  feeder,  140 

Reinforced  covers;  see  Belts  for  Conveyor, 
Rubber,  reinforced  covers, 

Repairs  and  replacements,  93,  252 

Return  idlers,  69,  70 

Return  run  of  belt  conveyor,  drip  from,  177, 
182,  183 

,  drive  on,  121,  130 

,  lumps  falling  on,  177,  181, 

197 

,  oil  on,  197 

,  tripper  pulleys  on,  181 

Reverse  bends  in  belt,  117,  120,  197 

"  R.  F.  &  C."  (rubber-filled  and  covered) 
belt,  52 

"  Rialto  "  bucket,  225,  228 

Ridgway,  John  J.,  belt  cleaner,  179 

— ,  — ,  double-belt  conveyor,  17 

— ,  — ,  hinged -edge  belt,  17,  44 

Rims  of  pulleys;  see  Pulleys^  (for  con- 
veyors, for  elevators). 

Robb  loading  hopper,  141 

Robins-Baldwin  tripper,  168 

Robins  Conveying  Belt  Co.,  14,  98,  99 

Robins-Hersh  tandem  drive,  120 

Robins,  Thomas,  11,  14 

Rock,  conveyor  for,  204 

— ,  elevator,  281 

Roller-bearing  idlers,  90,  91,  92,  93,  94,  95, 
106 


Roller-flight  conveyors,  compared  with  belt 

conveyor,  205 
Rolling  contact,  elevating  and  conveying 

by,  193 
Rolls  for  package  convt  yors,  185,  186;   see 

also  Idlers 
Rope  conveyor  belts,  63,  64 

—  elevator  belts,  209 
Rotary  belt  cleaners,  179 
Rouse  idler,  18 

Rubber,  aging,  22,  23,  29,  32,  36, 38, 44, 197, 
205 

—  belt;   see  Belts  for  Conveyors,  Belts  for 

Elevators. 
— ,  compounding  of,  21,  22 

—  covers;   see  Covers 
— ,  Para,  21,  22,  34 

— ,  plantation,  21,  22,  34 

—  substitutes,  21 
Rules,  worthless,  112,  222 

S 

St.  Clair  belt,  19 
Sacks,  conveyor  for,  184 
Safe  angle  of  incline  of  conveyor,  118,  142, 

143,  154 
Safety  devices  for  elevators,  276,  298,  304, 

305 

Sag  of  return  run  of  elevator  belt,  308 
"  Salem  "  bucket,  225,  229 
Salt,  elevator  for,  219 
Sand,  belt  for,  204 
— ,  wet,  in  tripper,  169 
Sandvik  steel  belt,  59,  60,  61 
Saturating  compounds  for  canvas  belt,  47, 

48,  184,  201,  255,  275 
Savings  due  to  improved  idlers,  93,  94 
"  Scandinavia  "  solid-woven  belt,  52 
Schidrowitz,  Philip,  on  "  Rubber  "  quoted, 

34 
Scoop  feed,  288 

—  loader,  188 

Scraper  for  cleaning  belt,  176 

discharging  from  belt,  158 

,  objections  to,  159 

,  traveling,  159 

pulley  rims,  122,  129,  180 

Scraping  coal  in  trough,  205 

Screen  chutes,  155,  156 

Screw  conveyor  compared  with  belt,  205 

—  take-up,  122,  131 
Seamed  buckets,  227 
Seamless  buckets,  209,  230 

Seams  in  assembling  duck,  15,  21,  22,  35,  37, 

40,  46 

Seam-strip,  21,  22,  40 
Selleck  belt,  17 

Separation  of  plies  in  service,  11,  23,  24,  32, 
159,  197,  199,  246,  248,  252,  289 
in  tests,  31,  35,  38;   see  also  Fric- 
tion Compound. 
Shelves,  belt  elevator  with,  320 
Ships,  distributing  coal  in,  190 


INDEX 


331 


Shop  splices,  32,  36,  40 
Short  belt  conveyors,  203,  204 
Shut-down,  allowance  for,    145,   146,    ^48, 

237 

Shuttle-belt  conveyors,  173,  174,  175,  176 
Sibley  idler,  80 
Side-feed  into  boot,  288 
Side-guide  idlers,  8,  13,  69,  70,  71,  80,  167, 
197 

,  injure  belt,  13,  71,  80,  167,  197 

Simplicity  of  idler  construction,  86,  88 
Single-plane  idler,  67 
Skewed  idler  pulleys,  80,  81 
Skip-hoists  instead  of  inclined  belts,  204 
Skirt-boards,  80,  137,  138,  150,  154,  197 

,  at  humps,  138 

,  design  of,  138 

Slack  belt,  disposal  of,  118 
Sliding  belts  in  a  trough,  6,  95 
Slip  of  conveyor  belt,  120,  123 

elevator  belt,  236,  246,  249,  252,  254, 

262,  267,  268,  275,  280,  302,  304 
Slip  of  material  on  inclined  belts,  69,  142, 

154 
Slow  speed  in  elevator  discharge,  220,  240, 

313,  314 

Slow  vulcanizing,  23 
Small  foot  wheel,  bad  effect  of,  214,  216, 

218,  219,  222,  246,  289,  303 
Smelter,  belt  elevators  in  a,  237,  238 
Snub  pulley,  117,  127,  128,  180 

,  as  tandem  pulley,  129 

Soft  edges  of  belts,  40 
Solid-woven  belts,  2k  50,  51,  54,  201 
Sorting  belts,  67,  193,  194,  195 
Southwark  Foundry  (Philadelphia),  7 
Spacing  of  buckets,  226,  227,  233,  234,  262 

,  inclined  elevators,  313 

—  idlers,  69,  70,  71,  72,  73,  74 
Spare  parts,  264 
Specifications  for  rubber  belts,  27,  28,  29, 

30,  31,  37,  38,  248 
,  comment  on,  32,  33,  34,  35,  36, 

37,  38,  39,  40 

,  Metcalf's,  30,  31 

,  Stewart's,  37,  38 

Speeds  for  belt  conveyors,   151,   152,  153, 

154, 155 
according  to  idler  construction, 

153 

,  excessive,  118,  197 

for  grain,  154 

inclines,  148,  154 

narrow  belts,  152 

packages,  187 

picking  and  sorting,  155 

,  maximum  and  minimum,  153, 

202 

,  steel  belt,  60 

Speeds  for  belt  elevators,  centrifugal,  211, 

212,  213,  215,  216,  217,  219, 

220,314 
,  continuous  bucket,  243,  244 


Speed  for  belt  elevators,  inclined,  243,  244, 

310,   312,  314 

limited    by    friability    of   ma- 
terial, 217 

wear  and  tear,  219 

.various    materials,    211,    212, 

216,  220 
Spill  at  foot  of  elevator,  245 

head  of  elevator,  213,  214,  221,  237, 

254, 269,  307,  309, 310, 311, 313, 315 

—  on  lower  run  of  belt  conveyor,  177,  182 
Splices,  belt  not  cut  square,  197,  199 

— ,  — ,  pulling  apart,  165 
— ,  — ,  shop,  32,  36,  40 

—  in  duck,  36,  37,  40,  41,  76 
Splitting  of  conveyor  belt,  15,  17, 36 
Spool  idlers,  8,  11,  69,  83 
Starting  belt  conveyor,  122 

,  under  load,  197 

Stearns  idler,  91 

Steel  belt,  59,  60,  61 

—  mesh  belt,  61,  62 

—  rope  belt,  63 

Steering  effect  of  idlers,  16,  78,  79 
Stephens-Adamson  Mfg.  Co.,  65,  69,  89,  90, 

98,  99,  165,  171,  182 
Stepped-ply  belt,  12,  15,  16,  24,  29,  76 
Stepped  splice,  59 

Stewart's  specifications  for  rubber  belt,  37, 
38 

,  comment  on,  38,  39,  40 

Stitched  canvas  belt;    see  Belts  for  Con- 
veyors, Belts  for  Elevator 
Stitched  rubber  belt,  23 
Stone  conveyor,  bad  design  of,  117 
—  elevator,  307,  309,  310 
Stop  for  travel  of  tripper,  169 
Straight-ply  belt,  16,  22 
Strength  of  belts,  52,  53,  54,  111 

due  to  filling  compound,  53 

Stresses,  internal,  in  belt,  81 

Stretch,  comparative,  48,  50,  53 

— ,  removal  of,  in  manufacture  of  belts,  21, 

40,  47,  50 
Strip  tests,  33,  39 
Stuart,  Francis  Lee,  belt  feeder,  140 

— , ,  discharge  devices,  172,  173 

Styles  in  belt  idlers,  65 
Substitutes  for  fabric  belts,  60 
rubber,  21 


Tables  of  horse-power  of  belt  conveyors, 
grease  lubrication,  100,  101, 102, 103, 104, 
105 

Tailings-stacker,  19,  24 

Take-up  tension  for  elevator  belt,  270,  274, 
277,  300,  301,  302,  307 

Take-up  travel,  amount  of,  292 

,  by  moving  the  boot,  286 

Take-ups  for  conveyors,  122,  129,  131,  132 

—  for  elevators,  210,  270,  274,  281,  283, 
284,  292,  295,  296,  298 


332 


INDEX 


Take-ups  for   conveyors,   automatic  270, 
274,  277,  295,  298,  300,  303 

,  separate,  285 

Tandem  drive,  advantages  of,  120 

,  belt  tensions  at,  120,  121,  132 

,  disadvantages  of,  120,  121 

for  belt  conveyor,  110,  119,  120,  121, 

129, 132 

,  large,  120 

on  return  run  of  belt,  121 

with  snub-pulley  as  driver,  129 

Tapered  roller  bearings  for  idlers,  95 
Tearing  of  rubber  covers,  30,  197,  199 
Temperature  alarm  for  hot  bearings,  298 
Tension  in  conveyor  belt  at  drive  pulley, 
108,  109,  110,  119,  122 

due  to  excessive  take-up,  197 

incline,  112 

,  working  unit  stress,   11,   112, 

117 

Tension  in  elevator  belt,  209,  210,  269,  270, 
271,  272,  273,  274,  275,  299, 
309 

due  to  take-up,  270,  274,  277, 

300,  301,  302,  307, 

,  working  unit  stress,  246,  274, 

310 
Tests  of  absorption  of  water  by  belts,  56 

effect  of  aging  of  rubber,  44,  45 

horse-power  of  conveyors,  90,  92,  93 

idler  spacing,  72,  73 

natural  curvature  of  rubber  belt,  74, 

75,76 

resistance  to  abrasion,  26,  27 

strength  of  duck,  33 

canvas  belt,  53 

finished  belt,  39 

friction  layer,  30,  31,  34,  35,  38 

rubber  compounds,  28 

Thickness  of  conveyor  belt,  108,  109,  110, 
114,  115 

,  maximum  and  minimum,  115 

elevator  belt,  274,  275 

rubber  covers,  22,  24,  26,  38,  41,  248, 

249,  250,  251 
Thomas  idler,  18 
Three-pulley  conveyor  drive,  127 

troughing  idler,  11,  13,  65,  6u,  67,  76, 

77,  82 
Throwing  machine,    for  run-of-mine   coal, 

190 

Throw-off  carriage,  5 
Ticknor  and  Baldwin  tripper,  164 
Tie-gum  construction  (rubber-belt),  24,  30, 

253 

Timken  Roller  Bearing  Co.,  95 
Torsion  at  conveyor  drive  shaft,  109 

elevator  head  shaft,  269 

Tower's  experiments  in  lubrication,  87 
Tractive  force  between  belt  and  pulley,  127; 

see  Friction,  coefficient  of, 
Trailer  extension  for  tripper,  167 
Training  belts,  68,  81 


Transfer  between  package  belt  conveyors, 
187 

—  chute,  136 

Trimming  coal  in  ships,  190 
Tripper,  4,  5,  156 

— ,  arrangement  for  return  run,  181 

—  brushes,  166,  180 

—  chutes,  166 

—  compared  with  plow  or  scraper,  159 

—  extension,  167,  171 
— ,  fixed,  7,  140,  160,  161 

— ,  — ,  injures  belt,  140,  160,  161,  197 

— ,  grain,  163 

— ,  invention  of,  7 

— ,  length  required  for,  169 

—  pulleys,  165,  167 

— ,  rails,  gage  of,  167,  199 
— ,  self-propelled,  8,  162,  164 
— ,  self-reversing,  162,  163 
— ,  traveling,  7,  8,  162 

—  with  by-pass  chute,  161 

haulage  rope,  167 

movable  pulley,  161 

— ,  worm-geared,  164 

Troughed  belt,  angle  of  troughing,  13,  15, 
16,  18,  79,  86,  145 

,  capacity  of,  143,  144,  147,  149 

Troughing,  angle  of,  13,  15,  16,  18,  79,  86, 
145 

— , ,  comparison  of,  79,  82,  86 

— ,  natural,  68 

— ,  shallow,  79,  81 

"  Turtle  "  belt-fastener,  57 

Two     belts,     conveying     and     elevating, 

between,  191 

Two-plane  troughing  idler,  10,  11,  65,  66 
Two-pulley  troughing  idler,  14,  68 

U 

Ultimate  strength  of  belts,  52,  53,  54,  111; 
see  Belts  for  Conveyors,  Belts  for  Eleva- 
tors. 

Undercure  in  vulcanizing,  44 
Uniroll  idler,  84,  85,  91,  146 
Unit  stress  in  conveyor  belt,  11,  112,  117 

elevator  belt,  246,  247,  310 

Universal  conveyor,  there  is  no,  205 


Vacuum  belt-cleaner,  180 

Vanner  belt,  43 

Vaughan  belt  conveyor,  19 

Voorhees  belt,  reinforced  cover,  19 

Vrooman  idler,  18 

Vulcanized  splice,  59 

Vulcanizing  belt,  21,  44 

W 

Warp  threads  (of  duck),  20,  46,  47,  50,  56 

Washeries,  belts  in,  201 

Washington  Avenue  Grain  Elevator,  8,  30, 

162 
Waste  from  picking  belts,  194,  195 


INDEX 


333 


Water,  absorption  of,  by  belts,  55,  56,  184 
Wear  on  belt  surface,  11,  12,  18,  19,  26,  f32, 

152,  153,  189,  249,  250;    see  Belts 

for  Elevators. 
elevator   belt   determines   thickness, 

274 

short  belts,  153 

Weather,  exposure  of  belts  to,  44,  46,  181, 

184,  197,  200 

Webster  and  Comstock  Mfg.  Co.,  14 
Webster  Mfg.  Co.,  65,  151 
Wedging  action  of  troughing  pulleys,  15 
Weight  of  belt,  balata,  51 

,  rubber,  41,  42 

,  solid- woven,  52 

,  stitched-canvas,  49 

buckets,  231,  232,  233 

Weighted  take-ups,  129,  132,  270,  295;  see 

Take-ups 

Weller  Mfg.  Co.,  67,  151,  171,  258 
Wentz,  J.  L.,  88,  188 
Westmacott,  P.  G.  B.,  7,  8,  134,  162 
Wet  coal,  belts  for,  199,  201 
—  elevators,  237,  238,  249,  251,  252,  253, 
278,  300 


Wet  grain,  elevator  belt  for,  248 

—  material,  pick-up  of,  235 
Whiting,  in  compounding  rubber,  21 
Wide  conveyor  belts,  tendency  toward,  18, 

82,86. 
Width  of  belts,  113,  114,  252,  253,  261 

loading  chutes,  113 

Winters  belt  cleaner,  179 
Wiper  for  belt  surface,  176 
Wire  mesh  belt,  61,  209 

—  reinforcement  for  fabric  belts,  19 

—  rope  belt,  63,  209 
Witherspoon-Englar  Co.,  296,  304 
"  Wooster  "  solid-woven  belt,  52 
Working  tensions  in  conveyor   belts,  111, 

112,  117 

elevator  belts,  246,  247,  310 

Wrap,  angle  of,  effect  of,  109,  110,  209,  308 


Zieber  idler,  66 

Zigzag  belt  conveyors,  204 

Zinc  oxide  in  compounding  rubber,  21 


UNIVERSITY  OF  ^CALIFORNIA  LIBRARY 
BERKELEY 

Return  to  desk  from  which  borrowed. 
This  book  is  DUE  on  the  last  date  stamped  below. 


JUL     H  1348 
SEP  2    19 


T  2  1950 
WAY  2  5  1950 


LD  21-100m-9,'47(A5702sl6)476 


530773 


Engineering 
Library 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


